RU2772115C2 - Use of inter-cellular growth due to multiplexing in wireless cellular systems - Google Patents

Abstract

FIELD: wireless communication.

SUBSTANCE: in a multi-antenna system (MAS) with multi-user (MU) transmissions (MU-MAS), at least one transceiver uses radio-frequency calibration to convert uplink channel state information (hereinafter – CSI) to downlink CSI. At the same time, at least one centralized processor uses CSI to calculate a set of pre-coding weight coefficients, generates a set of formed signals and transmits or receives a set of formed signals that are intentionally interfered to create a set of coinciding non-interfering data transmission lines with user devices within one and the same frequency range.

EFFECT: increase in network throughput.

44 cl, 12 dwg

Description

Right of priority

The present application claims the priority of co-pending U.S. Provisional Application No. 61/729,990, entitled "Systems and Methods for Exploiting Inter-Cell Growth by Multiplexing in Wireless Cellular Systems via Distributed Input-Distributed Output Technology", filed Nov. 26, 2012, which assigned to the assignee of this application. This application is incorporated herein by reference in its entirety.

Related Applications

This application may be related to the following pending US patent applications.

US Patent Application Ser. No. 13/233,006 entitled "System and methods for the planned development and obsolescence of the multi-user spectrum".

US Patent Application Ser. No. 13/232,996 entitled "Systems and Methods for Using Coherence Regions in Wireless Systems".

US Patent Application Ser. No. 13/464,648 entitled "System and Methods for Compensating Doppler Effects in Distributed Input-Distributed Output Systems".

U.S. Patent No. 8,542,763, issued September 24, 2013, entitled "Systems and methods for coordinating transmissions in distributed wireless systems through user clustering."

US Patent Application Ser. No. 12/802,988 entitled "Interference control, handover, power control and link adaptation in distributed input-distributed output (DIDO) communication systems".

U.S. Patent No. 8,170,081, issued May 1, 2012, entitled "System and Method for Adjusting Interference Suppression in DIDO Systems Based on Signal Power Measurements."

US Patent Application Ser. No. 12/802,974 entitled "System and Method for Controlling Inter-Cluster Handover of Clients Passing Through Multiple DIDO Clusters".

US Patent Application Ser. No. 12/802,989, entitled "System and Method for Controlling Client Handover between Different Distributed Input Distributed Output (DIDO) Networks Based on Client Rate Detection."

US Patent Application Ser. No. 12/802,958 entitled "System and Method for Power Control and Antenna Grouping in Distributed Input-Distributed Output (DIDO) Networks".

US Patent Application Ser. No. 12/802,975 entitled "System and Method for Adapting Links in Multi-Carrier DIDO Systems".

U.S. Patent No. 8,571,086, issued Oct. 29, 2013, entitled "System and Method for Precoding Interpolation in Multi-Carrier DIDO Systems."

US Patent Application Ser. No. 12/630,627, entitled "System and method for wireless communication with distributed antennas".

U.S. Patent No. 7,599,420, issued October 6, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,633,994, issued December 15, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,636,381, issued December 22, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 8,160,121, issued April 17, 2012, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,711,030, issued May 4, 2010, entitled "Spatially multiplexed troposcatter communication system and method."

U.S. Patent No. 7,418,053, issued August 26, 2008, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,885,354, issued Feb. 8, 2011, entitled "System and Method for Improving Communications with Near-Vertical Ionospheric Reflection Waves (NVIS) Using Space Time Coding."

State of the art

Over the past three decades, the wireless cellular market has seen an increase in subscribers around the world, accompanied by an increase in demand for higher quality services, with a shift from voice data to web browsing and real-time HD video streaming. This growing demand for services requiring higher data rates, lower latency, and improved reliability has spurred the radical development of wireless technologies through different standards, beginning with first-generation analog AMPS and TACS (for voice services) in the early 1980s, then digital standards GSM 2G and 2.5G, IS-95 and GPRS (for voice and data services) in the 1990s, 3G with support for UMTS and CDMA2000 technologies (for web browsing) in the early 2000s and, finally, the LTE standard (for high-speed Internet connection), which is currently being rolled out in various countries around the world.

The Long Term Evolution (LTE) standard is a standard developed by the 3rd Generation Systems Partnership Project (3GPP) for fourth generation (4G) wireless cellular systems. With LTE, downlink spectral efficiency can be achieved up to 4x over previous 3G and HSPA+ standards by utilizing the spatial components of the wireless channels through multiple input multiple output (MIMO) technology. The LTE-Advanced standard, which is currently under development, is an evolution of the LTE standard. It will achieve an 8-fold increase in spectral efficiency compared to 3G standard systems.

Despite this advancement in technology, it is highly likely that over the next three years, wireless communication systems will not be able to meet the growing need for data transfer speed associated with the growth of the smartphone and tablet market, which increasingly offers applications that process large data streams, such as real-time HD video streaming, video conferencing and gaming. According to estimates, in Europe in 2011-2015. Wireless network capacity will increase 5 times thanks to advanced technologies such as LTE, as well as the allocation of additional frequency band by the government [25]. For example, the Federal Communications Commission (FCC), as part of the National Broadband Development Plan for 2020, plans to release the 500 MHz band (of which 300 MHz will be available by 2015) to provide wireless Internet connectivity in the United States [24 ]. Unfortunately, according to forecasts for Europe [25], by 2015 the bandwidth usage will increase 23 times compared to 2011, and a similar bandwidth deficit in the USA is expected by 2014 [26–27]. Due to the need for such data processing, the income of wireless operators may be lower than their capital (CAPEX) and operating (OPEX) costs, which can potentially have a devastating impact on the wireless communications market [28].

Since the capacity gains provided by LTE deployment and range expansion are not sufficient, the only purported solution to avert the impending bandwidth crisis is to introduce new wireless technologies [29]. It is expected that the LTE-Advanced standard (development of the LTE standard) will provide additional growth compared to LTE through the use of advanced MIMO techniques, as well as by increasing the density of "small cells" [30]. However, there are limitations on the number of cells that can be placed in a certain area without interference problems or without increasing the complexity of the transport network for inter-cell coordination.

Brief description of the drawings

The patent or application file contains at least one color drawing. Copies of this patent or publication with color drawings are available from the United States Patent and Trademark Office upon request and upon payment of the required fees.

For the best understanding of the present invention, the following detailed description should be read in conjunction with the following drawings.

In FIG. 1 shows cells divided into a multiplexing area and a diversity area.

In FIG. 2 shows inter-cell interference in a variety of different areas.

In FIG. 3 shows an embodiment in which the transmit power from three base transceiver stations (BTS) transmitting simultaneously on the same frequency increases, resulting in a higher level of interference in the entire cell.

In FIG. 4 shows one embodiment in which a plurality of additional access points are added to deliberately increase the level of non-coherent signal interference throughout the cell.

In FIG. 5 shows a plurality of LTE network elements used in one embodiment of the present invention.

In FIG. 6a-6c provide detailed information related to LTE frames.

In FIG. 7a-b show a "resource element", which is the smallest modulation structure in LTE, which consists of one OFDM subcarrier in the frequency domain and one OFDM symbol duration in the time domain.

In FIG. 8 shows the SNR distribution for the practice deployment of one embodiment of the present invention in downtown San Francisco, California, USA.

In FIG. 9 shows the system architecture used in one embodiment of the present invention.

Detailed description

One solution to overcome many of the prior art limitations mentioned above is an implementation of distributed input-distributed output (DIDO) technology. DIDO technology is described in the following patents and patent applications, all of which are assigned to the assignee of this patent and incorporated herein by reference. These patents and applications are sometimes collectively referred to herein as "related patents and applications".

US Patent Application Ser. No. 13/233,006 entitled "System and methods for the planned development and obsolescence of the multi-user spectrum".

US Patent Application Ser. No. 13/232,996 entitled "Systems and Methods for Using Coherence Regions in Wireless Systems".

US Patent Application Ser. No. 13/475,598 entitled "Systems and Methods for Compensating Doppler Effects in Distributed Input-Distributed Output Wireless Systems."

U.S. Patent Application No. 13/464,648 entitled "Systems and Methods for Compensating Doppler Effects in Distributed Input-Distributed Output Systems."

U.S. Patent No. 8,542,763, issued September 24, 2013, entitled "Systems and methods for coordinating transmissions in distributed wireless systems through user clustering."

US Patent Application Ser. No. 12/802,988 entitled "Interference control, handover, power control and link adaptation in distributed input-distributed output (DIDO) communication systems".

U.S. Patent No. 8,170,081, issued May 1, 2012, entitled "System and Method for Adjusting Interference Suppression in DIDO Systems Based on Signal Power Measurements."

US Patent Application Ser. No. 12/802,974 entitled "System and method for managing inter-cluster handoff of clients that pass through multiple DIDO clusters."

US Patent Application Ser. No. 12/802,989, entitled "System and Method for Controlling Client Handover between Different Distributed Input Distributed Output (DIDO) Networks Based on Client Rate Detection."

US Patent Application Ser. No. 12/802,958 entitled "System and Method for Power Control and Antenna Grouping in Distributed Input-Distributed Output (DIDO) Networks".

US Patent Application Ser. No. 12/802,975 entitled "System and Method for Adapting Links in Multi-Carrier DIDO Systems".

U.S. Patent No. 8,571,086, issued Oct. 29, 2013, entitled "System and Method for Precoding Interpolation in Multi-Carrier DIDO Systems."

US Patent Application Ser. No. 12/630,627, entitled "System and method for wireless communication with distributed antennas".

U.S. Patent No. 7,599,420, issued October 6, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,633,994, issued December 15, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,636,381, issued December 22, 2009, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 8,160,121, issued April 17, 2012, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,711,030, issued May 4, 2010, entitled "Spatially multiplexed troposcatter communication system and method."

U.S. Patent No. 7,418,053, issued August 26, 2008, entitled "Distributed Input-Distributed Output Wireless Communication System and Method."

U.S. Patent No. 7,885,354, issued Feb. 8, 2011, entitled "System and Method for Improving Communications with Near-Vertical Ionospheric Reflection Waves (NVIS) Using Space Time Coding."

To reduce the size and complexity of this patent application, the disclosure of some related patents and applications is not explicitly presented below. For the full text of the description, please refer to related patents and applications.

One promising technology that could improve the spectral efficiency of wireless links by orders of magnitude, while still being free from the limitations of conventional cellular systems, is distributed input-distributed output (DIDO) technology (see related patents and applications listed above) . The present invention describes DIDO technology used in the context of cellular systems (such as LTE or LTE-Advanced), both within and without the limitations of cellular communication standards, to provide significant performance advantages over conventional wireless systems. First, a brief overview of MIMO technology and an analysis of the different spatial signal processing techniques that are used in the LTE and LTE-Advanced standards will be presented. It will then be demonstrated how the present invention provides significant throughput gains in next generation wireless systems over prior art approaches.

MIMO technology uses multiple antennas on the transmitter and receiver sides of a wireless link and applies spatial signal processing to improve link reliability through diversity techniques (i.e., increase gain through diversity), or provide higher data rates through multiplexing schemes (i.e. gain due to multiplexing) [1–2]. Diversity Gain is a measure of how resilient a signal is to fading, resulting in a higher signal-to-noise ratio (SNR) for a fixed bit rate. In multiplexing schemes, gain is provided by using additional spatial degrees of freedom of the wireless channel to increase the data rate with a fixed error probability. The basic conditions for diversity matching and multiplexing in MIMO systems were described in [3–4].

In practical MIMO systems, for dynamic switching between diversity and multiplexing schemes, depending on signal propagation conditions, communication link adaptation techniques can be used [20–23]. For example, the link adaptation schemes described in [22-23] show that in the low SNR mode or in the presence of channels with low spatial selectivity, it is preferable to use beamforming or orthogonal space-time block codes (OSTBC). On the contrary, spatial multiplexing can provide a significant increase in data rate over channels with high SNR and high spatial selectivity. For example, in FIG. 1 shows that cells can be divided into two zones: i) high SNR multiplex zone 101 (due to proximity to a cell tower or base station), where spatial channel degrees of freedom can be used to increase the data rate through spatial multiplexing; ii) a diversity area, or cell edge, 102, where spatial multiplexing techniques are not as efficient, and diversity techniques can be used to increase SNR and improve coverage (which result in only a modest increase in data rate). Note that in Fig. 1, in the macro cell circle, the shaded center circle represents the "multiplex area" 101 and the unshaded outer circle the "diversity area" 102. The same area markings are used in FIG. 1-4, where the shaded area is the "multiplex area" and the unshaded area is the "diversity area", even though they are not marked.

The LTE (version 8) and LTE-Advanced (version 10) standards define a set of ten transmission modes (TM), including either diversity schemes or multiplexing schemes [35, 85–86]:

• mode 1: single antenna port, port 0;

• mode 2: transmit diversity;

• Mode 3: High Cyclic Delay Diversity (CDD), Open Loop Spatial Multiplexing Extension for Single User MIMO (SU-MIMO);

• mode 4: spatial feedback multiplexing for SU-MIMO;

• mode 5: multi-user MIMO (MU-MIMO);

• mode 6: spatial feedback multiplexing using a single transmission layer;

• mode 7: single antenna port, UE specific reference signals (RS) (port 5);

• mode 8: single or double layer transmission with UE-specific RSs (ports 7 and/or 8);

• mode 9: closed-loop SU-MIMO using one to a maximum of eight layers (added in version 10);

• Mode 10: Multi-layer closed-loop SU-MIMO using a maximum of eight layers (added in Release 10).

The following describes the diversity and multiplexing schemes commonly used in cellular systems, as well as the specific techniques used in LTE systems, as summarized above, and their comparison with techniques unique to DIDO communication systems. First of all, two types of transmission methods are defined: i) intra-cell methods (using microdiversity in cellular systems) using multiple antennas to improve link reliability or data rate within a single cell; ii) inter-cell methods (using macro-diversity), which provide interaction between cells with additional diversity gain or multiplexing. Thereafter, it is described how the present invention provides significant advantages (including gains in bandwidth) over the prior art.

1. Intra-cell diversity methods

Intra-cell diversity techniques operate within a single cell and are capable of increasing SNR in low link quality scenarios (eg, in the case of users in the cell edge area receiving a signal from a central tower or base station with high propagation loss). MIMO communication systems use such typical diversity reception schemes as beamforming [5–11] and orthogonal space-time block codes (OSTBC) [12–15].

The LTE standard supports diversity techniques such as transmit diversity, rank 1 precoding with feedback, and dedicated beamforming [31–35]. The transmit diversity scheme supports two or four transmit antennas for the downlink (DL) and only two antennas for the uplink (UL). In the DL channel, it is implemented by space frequency block codes (SFBC) combined with frequency hopping transmission diversity (FSTD) to exploit space and frequency selectivity [31]. Rank 1 precoding makes it possible to create a dedicated beam to one user based on quantized weights selected from a codebook (previously created using limited feedback techniques [36–42]) in order to reduce the cost associated with providing feedback from user equipment (UE) to a base transceiver station (BTS or eNodeB in LTE terminology). Alternatively, dedicated beamforming weights may also be calculated based on a specific UE reference.

2. Intracellular multiplexing methods

MIMO multiplexing schemes [1, 19] provide an increase in data rate in high SNR mode and in scenarios with a sufficient number of spatial degrees of freedom in the channel (for example, in the case of environments with high levels of multipath propagation and spatial selectivity [16–18]) to maintain a plurality of parallel data streams over wireless communication lines.

The LTE standard supports different multiplexing techniques for single user MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO) [31]. SU-MIMO schemes have two modes of operation: i) closed-loop mode, which uses response information from the user equipment (UE) to select DL precoding weights; ii) open-loop mode applied when no feedback is available from the UE or when the UE is moving too fast to support the closed-loop schemes. Feedback schemes use a set of pre-calculated weights selected from the codebook. These weights can support two or four transmit antennas and one to four parallel data streams (defined by the number of layers of the precoding matrix) depending on the request of the UE and the decision made by the scheduler at the BTS. LTE-Advanced will include new transmission modes up to MIMO 8x8 with the ability to achieve a maximum increase in spectral efficiency of 8 times through spatial signal processing [62].

MU-MIMO schemes are defined for both UL and DL channels [31, 50]. With regard to UL, each UE sends a reference signal to the BTS, consisting of a cyclically shifted version of the Zadoff-Chu sequence [33]. These reference signals are orthogonal so that the BTS can estimate the channel from all UEs and demodulate the data streams from multiple UEs simultaneously through spatial processing. On the DL link, precoding weights for different UEs are selected from codebooks based on feedback from the UE and the scheduler (similar to closed loop SU-MIMO schemes), and only rank 1 precoding is allowed per UE (e.g., each UE only receives one data stream).

Intra-cell multiplexing techniques that use spatial processing provide satisfactory performance only in propagation scenarios characterized by high SNR (or SINR) and high spatial selectivity (high multipath environments). In conventional macro cells, these conditions can be difficult to achieve since BTSs are typically located far from UEs and the SINR distribution tends to be centered at low values [43]. In these scenarios, MU-MIMO schemes or diversity techniques may be a better choice than SU-MIMO with spatial multiplexing.

Other techniques and network solutions expected to be used in LTE-Advanced to gain additional multiplexing gains (not requiring MIMO spatial signal processing) are carrier aggregation (CA) and small cells. CA [30, 44–47] combines different parts of the radio frequency (RF) band to extend the signal bandwidth up to 100 MHz [85], thus giving higher data rates. In-band CA combines different bands within the same part of the band. Thus, it can use the same RF chain for multiple channels, and multiple data streams are recombined by software. With interband CA, operation in different parts of the band requires different RF circuits and signal processing to recombine multiple data streams from different bands.

The main idea of small cells [30, 47] is to reduce the size of conventional macro cells, which provides higher cell density and throughput per coverage area. Typically, small cells are deployed using inexpensive access points with low transmission power (as shown in Fig. 1), as opposed to the expensive high cell towers used in macro cells. LTE-Advanced defines two types of small cells: i) outdoor metro cells in urban areas that support 32 to 64 users simultaneously, and ii) indoor femtocells that serve up to 4 active users. One of the advantages of small cells is that the density of UEs close to the BTS is statistically higher, resulting in a better SNR than can be obtained through spatial multiplexing to increase the data rate. However, many issues related to the practical deployment of small cells, especially issues related to the transport network, still need to be addressed. In reality, accessing the BTS of each small cell via high-speed wired connections can be a challenge, especially given the high density of metro and femto cells in a given coverage area. Although a line-of-sight (LOS) transport network for small cells can often be implemented cost-effectively compared to a wired transport network, there are often no practical ways to establish a LOS transport network at the preferred locations of small cell BTSs, as well as a general non-line-of-sight wireless transport network solution ( NLOS) for small cell BTS. Finally, complex real-time coordination between BTSs of small cells is required to avoid interference, as occurs in self-organized networks (SON) [30, 51–52], and to use sophisticated cell scheduling tools (even more complex than in conventional cellular networks). systems, due to the higher density of small cells) to plan their optimal placement [48,49].

It is easy to show that there is no practical general solution that would ensure the coexistence of small cells with macro cells and optimal or necessarily evenly increased throughput. Among many such unresolvable situations, there is one where a small cell is located such that its UEs inevitably overlap with the transmission in the macro cell, and the small cells and macro cells use the same frequencies to address the respective UEs. In this situation, it is obvious that the macro cell transmission will interfere with the small cell transmission. While there may be an approach that limits such interference to specific conditions for a particular macro cell, a particular small cell, the particular macro cell and small cell UEs involved, the throughput requirements of those UEs, and propagation environment conditions; any of these approaches would be highly specific not only for the static macro cell and small cell design, but also for the dynamic conditions of a particular time slot. Typically, it is not possible to achieve the full channel throughput to each UE.

3. Inter-cell diversity methods

Inter-cell transmission techniques enable interaction between BTSs to improve the performance of wireless networks. These techniques are a special case of the methods listed in related patents and applications that allow wireless transceivers to interact in a generally distributed antenna network for multiple UEs, all of which use the same frequency at the same time. The interaction between BTSs to eliminate inter-cell interference in the specific case of cellular systems for one UE at a given time at a given frequency has been described in [53]. In the system described in [53], each macro cell was subdivided into a plurality of subcells and soft handover between subcells was provided using dedicated beamforming from coordinated BTSs to improve link reliability at one UE and at one frequency as it moved along subcell boundaries.

Recently, this class of interoperable wireless cellular networks has been defined in the MIMO literature as a "network MIMO" or "coordinated multipoint" (CoMP) system. Theoretical analysis and modeling of the results of the benefits obtained in network MIMO by eliminating inter-cell interference are presented in [54–61]. A key benefit of network MIMO and Coordinated Multipoint Multipoint (CoMP) is the elimination of inter-cell interference in the overlapping cell areas 201-203 shown in FIG. 2.

CoMP networks are being actively introduced into the LTE-Advanced standard as a solution to limit intercellular interference in next generation cellular networks [62–64]. So far, two CoMP solutions have been proposed for inclusion in the standard to eliminate inter-cell interference: i) coordinated scheduling/beamforming (CS/CB), where the UE receives its data stream from only one BTS through beamforming, and coordination between BTSs is allowed for interference elimination by beamforming or planning techniques; ii) joint processing (JP), where data for a given UE is jointly transmitted from multiple BTSs to improve received signal quality and eliminate inter-cell interference. CoMP-JP provides more gain than CoMP-CS/CB at higher costs in the transport network to coordinate between BTSs.

4. Inter-cell multiplexing methods

Prior art multi-user wireless systems add complexity and limitations to wireless networks, whereby a given user's experience (eg, available bandwidth, latency, predictability, reliability) is affected by the fact that other users within an area are using the band. Considering the growing demand for aggregate bandwidth within the range of wireless communication shared by multiple users, as well as the growing number of applications based on the reliability, predictability and low latency of a multi-user wireless network for a given user, it is clear that prior art multi-user wireless communication technology has many restrictions. Indeed, with limited availability of spectrum suitable for certain types of wireless communications (e.g., wavelengths that can efficiently penetrate building walls), prior art wireless methods will not be sufficient to meet the growing demand for bandwidth that is reliable, predictable, and has low delay.

Prior art diversity and multiplexing techniques can theoretically provide a maximum of 4x throughput improvement in current cellular networks for LTE (via 4x4 MIMO) or theoretically a maximum of 8x for LTE-Advanced (via 8x8 MIMO), although higher MIMO orders give a decreasing throughput gain in a given multipath environment, in particular as UEs (eg, smartphones) become smaller and more limited in terms of antenna placement. Other modest capacity gains in next generation cellular systems can be achieved by allocating additional band (e.g., under the FCC's National Broadband Plan) through carrier aggregation techniques and denser distribution of BTS through small cell networks and SON. [30, 46]. However, all of the above techniques still rely heavily on band sharing or time sharing techniques in multi-user transmissions because the spectral efficiency gains provided by spatial signal processing are limited.

Although the inter-cell methods of the prior art (eg, MIMO and CoMP network systems [53-64]) can improve the reliability of cellular networks by eliminating inter-cell interference, they provide only marginal throughput gains. In fact, in these systems, the power transmission from each BTS is limited within the boundaries of the cell, so due to the reduction in power between cells, they are only effective in eliminating inter-cell interference. In FIG. 2 shows one example of cellular networks with three BTSs 210-212, each with its own coverage area or cell. The power transmitted from each BTS 210-212 is constrained to limit interference between cells in the areas shown in FIG. 2 are shown as honeycomb overlap areas. Since these systems operate in the low SINR mode in the interference zone, they provide only a small increase in spectral efficiency, similar to intra-cell schemes for SU-MIMO. In order to really achieve significant throughput gains in inter-cell networks, it is necessary to relax the power limitation at cell boundaries and ensure that spatial multiplexing techniques are applied across the entire area of high SINR cells (not just at the edge of a low SINR cell, as in prior art approaches). ).

Thus, it would be desirable to provide a system that improves spectral efficiency by orders of magnitude by removing any restrictions on the power transmitted from distributed BTSs and exploiting inter-cell gain by multiplexing through spatial processing. In FIG. 3 shows a case of increasing the power transmitted from three BTSs 301-303 simultaneously on the same frequency, thus giving a higher level of interference throughout the cell. In prior art systems, such interference would result in non-coherent interference (breaking signal reception at the UE) in BTS interference zones, but this interference is actually exploited in embodiments of the present invention by applying innovative inter-cell multiplexing techniques with spatial signal processing to create coherent interference zones ( UE-enhancing signal reception) around each UE, thus providing simultaneous non-interfering data streams to each UE and increasing their SINR throughout the cell.

In one embodiment of the present invention, this gain due to inter-cell multiplexing is achieved using distributed input-distributed output (DIDO) systems [0014-0020] and [77-78]. In FIG. 4 shows one example in which a plurality of additional access points 401 are added to deliberately increase the level of non-coherent interference throughout the cell, which is used in the present invention to generate zones of coherent interference around the UE and gain due to inter-cell multiplexing. Such additional BTSs can be low power transceivers similar to low-cost Wi-Fi access points, thus providing smaller coverage areas overlapping throughout the macro cell as shown in FIG. 4.

It can be seen that in prior art inter-cell methods, non-coherent interference is prevented by intentionally limiting the transmit power from each BTS 210-212, as shown in FIG. 2, and residual inter-cell interference (in overlapping regions between cells) is eliminated through spatial processing, thus improving SINR and inter-cell diversity gain. On the contrary, in the present invention, non-coherent interference is used to create coherent interference around the UE by transmitting more power from each BTS. This makes it possible to improve signal quality at the UE, which is a necessary condition for obtaining inter-cell gain by multiplexing over the entire cell through spatial processing. Thus, the systems described in the prior art cannot be applied to achieve inter-cell gain by multiplexing through spatial processing, since the signal quality over the entire cell area is insufficient (due to transmission power limitation from the BTS) in order to be able to use the methods inter-cell multiplexing applied in the present invention. Moreover, with the systems described in the prior art, it would not be possible to achieve the gain due to the multiplexing obtained in the present invention, as shown in FIG. 3-4, given that prior art systems were designed to prevent inter-cell interference within the separation zones shown in the shaded area in FIG. 1-4, and not for the purpose of using inter-cell interference in multiplexing areas to obtain through multiplexing inter-cell gain, which is achieved in the present invention.

Embodiments of the present invention include a system and methods for utilizing inter-cell gain by multiplexing in wireless communication networks through spatial processing using a multi-antenna system (MAS) with multi-user (MU) transmissions (multi-user multiple-antenna system, or MU-MAS). In one embodiment of the present invention, the power transmitted from multiple antennas is limited to minimize interference at cell boundaries (as in conventional cellular systems), and spatial processing techniques are used only to eliminate inter-cell interference. In another embodiment of the present invention, the power transmitted from multiple antennas is not limited to any particular power level (as long as the power emission level does not exceed legal or safety limits), thus creating intentionally higher power levels throughout the cell. levels of inter-cell interference, which is used to achieve inter-cell gain through multiplexing and increasing the throughput of the wireless communication network.

In one embodiment, the wireless communications network is a cellular network, as shown in FIG. 1-2, such as a cellular network based on LTE standards. In another embodiment of the present invention, the wireless communication network is not limited to any particular cell layout, and cell boundaries may cover larger areas, as in FIG. 3–4. For example, the wireless communications network may be a wireless local area network (WLAN) or a mesh ad hoc or sensor network, a distributed antenna system, or a DIDO system with access points placed intuitively without any power transmission restrictions. But the general applicability of the present invention to wireless communication networks is not limited to such examples of network structures. The present invention is applicable to any wireless network in which multiplexing gain is achieved by transmitting signals from multiple antennas that interfere when received by multiple UEs, creating simultaneous non-interfering data streams to multiple UEs.

As shown in FIG. 9, one embodiment of a MU-MAS consists of a centralized processor 901, a base station network (BSN) 902, and M base transceiver stations (BTS) 903 communicating wirelessly with N client devices, also referred to as UEs (shown as UEs 1- 4). The central processing unit 901 receives N streams of information over a network 900 (for example, over the Internet) with different network content C1-5 (for example, video, web pages, video games, text, voice data, etc., the stream of which originates from web servers or other network sources) intended for different client devices UE 1-4. In the following, the term "information stream" refers to any data stream sent over the network 900 containing information that can be demodulated or decoded as a separate stream in accordance with a certain modulation/coding scheme or protocol to form any data, including, without limitation, audio -, web and video content. In one embodiment, the information stream is a bit sequence having network content that can be demodulated or decoded as a separate stream.

The CPU 901 uses transform precoding to combine (in accordance with algorithms such as those described in related patents and applications) N streams of network content information into M bit streams. By way of example, and not limitation, transform precoding can be linear (e.g., vanishing of insignificant coefficients [65], block diagonalization [66–67], matrix inversion, etc.) or non-linear (e.g., coding dirty paper [68–70] or Tomlinson-Harashima precoding [71–72], trellis coding technique, or Trellis modulation [73–74], vector coding technique [75–76]). Hereinafter, the term "bitstream" refers to any sequence of bits that does not necessarily contain useful data bits and which therefore cannot be demodulated or decoded as a separate stream for network content recovery. In one embodiment of the invention, the bitstream is a complex baseband signal that is generated by a centralized processor and quantized with a predetermined number of bits for transmission to one of the M transceiver stations.

In one embodiment, the MAS is a distributed input-distributed output (DIDO) system described in related patents and applications. In this embodiment, the DIDO system consists of the following.

• User Equipment (UE) 1-4. RF transceiver for fixed or mobile clients receiving data streams via the downlink (DL) channel of the DIDO transport network and transmitting data to the DIDO transport network via the uplink (UL) channel.

• Base transceiver station (BTS) 903. The BTSs communicate with the DIDO transport network via a wireless channel. BTSs in one embodiment are access points consisting of a DAC/ADC and a radio frequency (RF) circuit to convert the baseband signal to RF. In some cases, the BTS is a simple RF transceiver equipped with a power amplifier/antenna, and the RF signal is transmitted to the BTS via the RF Link over Fiber technology described in related patents and applications.

• Controller (CTR) 905. CTR 905 is a specific type of BTS designed to perform special functions such as transmitting training signals to synchronize the BTS and/or UE in time/frequency, receiving/transmitting control information from/to UE, receiving information channel state information (CSI) or channel quality information from the UE. One or more CTR stations can be included in any DIDO system. If multiple CTRs are available, the information transmitted to or received from these stations can be combined to increase diversity and improve link quality. In one embodiment, CSI is received from a plurality of CTRs via maximum ratio combining (MRC) techniques to improve CSI demodulation. In another embodiment, control information is sent from a plurality of CTRs by maximum ratio signaling (MRT) to improve the SNR at the receiver side. The scope of the invention is not limited to MRC or MRT techniques, and any other diversity method (eg, antenna selection, etc.) can be used to improve the quality of the wireless links between the CTR and the UE.

• Centralized Processing Unit (CP) 901. The CP is a DIDO server that communicates with the Internet or other types of external networks via the DIDO transport network. In one embodiment, the CP performs DIDO baseband signal processing calculations and sends the generated signals to distributed BTSs for transmission over DL.

• Base Station Network (BSN) 902. The BSN is a network that connects CPs and distributed BTSs and transmits information on either a DL channel or a UL channel. The BSN is a wired network, a wireless network, or a combination of both. For example, a BSN is a DSL, cable, fiber optic, or wireless link with or without line of sight. Moreover, a BSN is a private network, a local area network, or the Internet.

The following describes how the structure of the above DIDO system can be built into the LTE standard for cellular systems (as well as for non-cellular systems that use LTE protocols) to achieve additional spectral efficiency gains. First, an overview of the LTE structure and modulation techniques used in DL and UL channels will be presented. Then, a brief description of the physical layer frame structure and resource allocation in the LTE standard will be given. Finally, DIDO precoding methods for downlink (DL) and uplink (UL) channels in multi-user scenarios in which the LTE framework is applied will be defined. For DL circuits, two solutions have been proposed: open-loop and closed-loop DIDO circuits.

LTE is designed based on a flat network architecture (as opposed to the hierarchical architecture of previous cellular standards) to achieve delay reduction, packet loss reduction via ARQ, connection setup time reduction, coverage enhancement and throughput enhancement via macro diversity. In FIG. 5 shows the following network elements of LTE networks [79].

- GW (gateway) 501-502 is a router that connects the LTE network with external networks (for example, the Internet). The GW is divided into a Serving Gateway (S-GW) 502, which terminates the E-UTRAN interworking, and a PDN Gateway (P-GW) 501, which provides interworking with external networks. S-GW 502 and P-GW 501 are part of the so-called Evolved Packet Core (EPC).

- MME (Mobility Management Node) 503 manages the mobility, security parameters and identity of the UE. MME 503 is also part of EPC LTE.

- eNodeB (Evolved Node-B) 504 is a base station that performs radio resource management, user mobility and scheduling.

- UE (user equipment) 505 - mobile stations.

In one embodiment of the present invention, the LTE network is a DIDO network, wherein DIDO-UE is a UE in LTE networks, DIDO-BTS is an LTE eNodeB, DIDO-CTR is an LTE eNodeB or MME, DIDO-CP is an LTE GW .

The LTE frame duration is 10 ms, and the frame consists of ten subframes, as shown in FIG. 6a–c [33, 80]. Each subframe is divided into two slots of 0.5 ms each. The LTE standards define two types of frames: i) Type 1 for FDD operation as shown in FIG. 6a, in which all subframes are assigned to either downlink (DL) or uplink (UL) channels; ii) Type 2 for TDD operation as shown in FIG. 6b, in which part of the subframes are assigned to DL and part to UL (depending on the selected configuration), while several subframes are reserved for "special use". Each frame contains at least one special subframe, which consists of three fields: i) downstream pilot time slot (DwPTS) reserved for DL transmission; ii) guard interval (GP); iii) upstream pilot timeslot (UpPTS) for UL transmission.

LTE uses orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFMDA) modulation for DL and single carrier FDMA (SC-FDMA) for UL. A "resource element" (RE) is the smallest modulation structure in LTE and consists of one OFDM subcarrier in frequency and one OFDM symbol duration in time, as shown in FIG. 7. A "resource block" (RB) consists of 12 frequency subcarriers and one 0.5 ms time slot (consisting of 3 to 7 OFDM symbols depending on the DL to UL channel ratio and cyclic prefix type).

1. DIDO Downlinks with Loopback in LTE

Closed-loop DIDO schemes can be used in either time division duplex (TDD) or frequency division duplex (FDD) systems. In FDD systems, the DL and UL channels operate on different frequencies, so DL channel state information (CSI) estimation must be performed on the UE side and transmitted back to the CP via the BTS or CTR via the UL link. In TDD systems, the DL and UL channels are tuned to the same frequency and the system can use either closed-loop techniques or open-loop schemes that use channel reciprocity (as described in the section below). The main disadvantage of feedback schemes is the need for them to receive feedback, which leads to an increase in the cost of control information according to the UL.

One embodiment of the mechanism for feedback schemes in DIDO systems is as follows: i) BTS 903 send signaling information to the UE over DL; ii) UEs use this signaling information to evaluate DL channel state information (CSI) from all "active BTSs"; iii) UEs quantize the CSI DL or apply codebooks to select precoding weights to be used for the next transmission; iv) the UEs send the quantized CSI or codebook index to the BTS 903 or CTR 905 via the UL channel; v) BTS 903 or CTR 905 send information to CSI or codebook index to CP 901 which calculates precoding weights for data transmission over DL. "Active BTS" is defined as the set of BTSs available for a given UE. For example, in the related co-pending US patent application ser. No. 12/802,974, entitled "System and Method for Controlling Inter-Cluster Handoff of Clients Passing Through Multiple DIDO Clusters", and related co-pending US Patent Application Ser. No. 12/917,257 entitled "Systems and methods for coordinating transmissions in distributed wireless systems through user clustering", a "user cluster" is defined as a set of BTSs available to a given UE. The number of active BTSs is limited by the user cluster to reduce the number of CSIs from BTS to a given UE for which estimation is required, thus reducing the cost of UL feedback and the complexity of DIDO precoding calculations on the CP 901.

1.1 DIDO downlink signaling under the LTE standard

The LTE standard defines two types of reference signals (RS) that can be used for DL signaling in closed loop schemes [33, 50, 82-83]: i) cell specific reference signal (CRS); ii) a UE-specific reference signal, such as a channel state information reference signal (CSI-RS) and a demodulation RS (DM-RS). The cell-specific RS is not precoded, while the UE-specific RS is precoded [50]. CRS is applied in LTE Release 8, which uses codebook-based SU/MU-MIMO techniques, and each cell contains a maximum of four antennas. LTE-Advanced Release 10 supports non-codebook based SU/MU-MIMO schemes with a maximum of eight transmit antennas, as well as CoMP schemes with antennas distributed over different cells. Thus, version 10 allows for greater flexibility in signaling schemes via CSI-RS. The present invention describes how each type of signaling scheme can be used in DIDO systems to provide precoding.

1.1.1 Signaling in DIDO using CRS

CRS is used in LTE systems (version 8) to estimate the CSI from all BTS transmit antennas at the UE [80, 84]. The CRS is obtained as the product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random number (PRN) sequence. There are three orthogonal and 170 possible PRN sequences, making a total of 510 different CRS sequences. Each sequence uniquely identifies one cell. The CRS is transmitted within the first and third to last OFDM symbol of each slot, as well as every sixth subcarrier. For each BTS transmit antenna, time and frequency orthogonal models are developed for a unique CSI estimate from each of the four antennas at the UE. This high density of CRS in time and frequency (i.e. signal routing in each slot of 0.5 ms and with every sixth subcarrier), providing 5% of the cost, was designed intentionally to support scenarios with fast channel changes in time and frequency [ 83].

In practical DIDO systems, it may be that each UE "sees" more than four BTSs in its user cluster. For example, in FIG. 8 shows the SNR distribution for DIDO deployment in practice in downtown San Francisco, California, USA. The propagation model is based on the 3GPP propagation/shadowing loss model [81] and assumes a carrier frequency of 900 MHz. The dots on the map indicate the location of the DIDO-BTS, while the dark circle represents the user cluster (in which the UE is placed in the center of the circle). In sparsely populated areas, the UE "sees" only a few BTSs within its user cluster (eg, a total of three BTSs in the example of FIG. 8), while in densely populated areas, each user cluster can contain up to 26 BTSs, as in FIG. eight.

High CRS redundancy can be used in DIDO systems to provide CSI estimates from any number of transmit antennas greater than four. For example, if the channel is fixed and wireless or has low Doppler effects, it is not necessary to calculate the CSI from all four transmit antennas every 0.5 ms (slot duration). Similarly, if the channel has a uniform frequency, the CSI estimate with every sixth subcarrier is redundant. In this case, the resource elements (RE) occupied by the redundant CRS can be re-allocated to other transmit antennas or BTSs in the DIDO system. In one embodiment of the present invention, the system allocates redundant CRS resource elements to additional antennas or BTSs in a DIDO system. In another embodiment, the system estimates channel time and frequency selectivity and dynamically allocates CRS for different BTSs or only for BTSs within a user cluster for different resource elements.

1.1.2 DIDO signaling using CSI-RS and DM-RS

In LTE-Advanced (version 10), CSI-RS is applied by each UE to estimate CSI from BTS [33, 83]. The standard defines an orthogonal CSI-RS for different transmitters on a BTS so that a UE can distinguish between CSIs from different BTSs. CSI-RS supports a maximum of eight transmit antennas per BTS as in tables 6.10.5.2-1.2 in [33]. CSI-RS is sent at intervals ranging from 5 to 80 subframes (ie CSI-RS is sent every 5-80 ms) as in Tables 6.10.5.3-1 in [33]. The CSI-RS periodicity in LTE-Advanced was intentionally set to a higher value than CRS in LTE to avoid excessive control information overhead, especially for legacy LTE terminals that cannot use these additional resources. Another reference signal used for CSI estimation is RS demodulation (DM-RS). DM-RS is a demodulation reference signal dedicated to a specific UE and transmitted only on a resource block assigned for transmission to that UE.

When there are more than eight antennas within a user cluster (the maximum number of transmitters supported by the LTE-Advanced standard), alternative techniques must be used to achieve DIDO precoding to ensure system compliance with the LTE-Advanced standard. In one embodiment of the present invention, each UE uses CSI-RS or DM-RS or a combination of both to estimate CSI from all active BTSs in its own user cluster. In the same embodiment, the DIDO system detects the number of BTSs within the user cluster as well as the compliance of the user cluster with the LTE-Advanced standard (which supports up to eight antennas). In the event of a mismatch, the DIDO system uses alternative techniques to ensure DL signaling from the BTS to the current UE. In one embodiment, the power transmitted from the BTS is reduced until no more than eight BTSs are reachable by the UE within its user cluster. However, this solution, due to the reduction in coverage area, may reduce the data rate.

Another solution is to divide the BTS in the user cluster into subsets, and send one set of CSI-RS at a time for each subset. For example, if the CSI-RS periodicity is 5 subframes (ie 5 ms) as in Table 6.10.5.3-1 in [33], then every 5 ms a CSI-RS is sent from a new BTS. It should be noted that this solution works as long as the CSI-RS periodicity is small enough to cover all subsets of BTSs within the UE's channel coherence time (which is a function of the UE's Doppler velocity). For example, if the selected CSI-RS periodicity is 5 ms and the channel coherence time is 100 ms, a maximum of 20 BTS subsets of 8 BTS each can be defined, adding a total of 160 BTS maximum within a user cluster. In another embodiment of the present invention, the DIDO system estimates the UE coherence time and decides how many BTSs can be supported within a user cluster for a given CSI-RS periodicity to avoid performance degradation due to channel changes and Doppler effect.

All proposed solutions for CSI-RS comply with the LTE standard and can be deployed within the framework of conventional LTE systems. For example, the proposed method, which allows more than eight antennas per user cluster, would require no modifications to the LTE UE equipment and software implementation, and only a slight change in the protocols used on the BTS and CP to select a subset of BTSs at any given time. These modifications can be easily implemented on a cloud-based Software Defined Radio (SDR) platform, which is one of the promising deployment examples for DIDO systems. Alternatively, if it is possible to relax the limitations of the LTE standard, slightly modified hardware and software for LTE UEs can be developed to support similar but non-LTE compliant DIDO modes of operation, so that UEs can operate in full LTE compliance mode or in a modified mode that supports operation of DIDO systems that do not comply with LTE requirements. For example, another solution is to increase the number of CSI-RSs to provide more BTSs in the system. In another embodiment of the present invention, different models and periodicities for CSI-RS are used as a means of increasing the number of supported BTSs per user cluster. Such minor modifications to the LTE standard can be small enough to allow existing UE LTE chipsets to be used with a simple software modification. Or, if you need to modify the hardware of the chipsets, the changes will be small.

1.2 Feedback methods using CSI in DIDO uplink under the LTE standard

In LTE and LTE-Advanced, the UE sends feedback information to the BTS to report its current channel conditions and precoding weights for DL feedback transmission. Three different channel metrics are included in these standards [35].

- The Rank Index (RI) indicates how many spatial streams are transmitted to a given UE. This number is always equal to or less than the number of transmitting antennas.

- The Precoding Matrix Index (PMI) is a codebook index used for precoding on the DL channel.

- The channel quality index (CQI) defines a modulation coding and forward error correction (FEC) scheme to be applied over the DL in order to maintain a predetermined error rate for given channel conditions.

Only one RI is noted for the entire bandwidth, while PMI and CQI transmission may be wideband or may be provided for a subband, depending on the frequency selectivity of the channel. These metrics are carried in the UL over two different types of physical channels: i) an uplink physical control channel (PUCCH) used for control information only; ii) a common uplink physical channel (PUSCH) used for both data and control information, allocated per resource block (RB) on a per subframe basis. In PUCCH, the RI, PMI and CQI transmission procedure is periodic and the metrics can be either wideband (for channels with uniform frequency) or selectable by the UE on a subband basis (for channels with frequency selectivity). In PUSCH, the feedback procedure is aperiodic and may be selected by the UE on a subband basis (for channels with frequency selectivity) or be configured at a higher level on a subband basis (eg, for transmission mode 9 in LTE-Advance with eight transmitters).

In one embodiment of the present invention, the DIDO system uses RI, PMI, and CQI to convey its current channel state and BTS and CP precoding information. In one embodiment, the UE uses the PUCCH to transmit these metrics to the CP. In another embodiment, if more metrics are required for DIDO precoding, the UE uses PUSCH to send additional metrics to the CP. If the channel has a flat frequency, the UE can use additional UL resources to transmit PMI to more antennas in DIDO systems. In one embodiment of the present invention, the UE, BTS, or CP evaluates the frequency selectivity of the channel, and if the channel has a flat frequency, the UE uses additional UL resources to transmit PMI to more BTSs.

2. DIDO Downlinks Open Loop in LTE

Open loop DIDO schemes can only be used in time division duplex (TDD) systems that use the principle of channel reciprocity. One embodiment of the mechanism for open loop schemes in DIDO systems is as follows: i) UEs 1-4 send signaling information to BTS 903 or CTR 905 on UL; ii) BTS 903 or CTR 905 use this signaling information to estimate UL CSI from all UEs 1-4; iii) BTS 903 or CTR 905 use RF calibration to convert CSI UL to CSI DL; iv) BTS 903 or CTR 905 forward the CSI DL or codebook index to the CP via BSN 902; v) The CP 901 calculates the precoding weights for the DL data transmission based on this DL CSI. Similar to closed loop DIDO schemes, user clusters can be used to reduce the number of CSI from the UE estimated per BTS, thus reducing the computational load on the BTS as well as the amount of signaling information that needs to be transmitted over the UL. In one embodiment of the present invention, precoding techniques for open loop systems are used to direct simultaneous non-interfering data streams from a BTS to a UE over a DL channel.

In LTE, there are two types of uplink reference signals [31, 33, 87]: i) sounding reference signal (SRS) used for link scheduling and adaptation; ii) the demodulation reference signal (DMRS) used to receive the data. In one embodiment of the present invention, SRS or DMRS is used in open loop DIDO systems to estimate UL channels from all UEs to all BTSs. In the time domain, DMRS is sent with the fourth OFDM symbol (using the normal cyclic prefix) of each LTE slot (0.5 ms duration). In the frequency domain, the DMRS directed on the PUSCH is associated for each UE with the same resource block (RB) used by that UE for data transmission on the UL.

The length of the DMRS is M ^RS = mN ^RB where m is the number of RBs and N ^RB = 12 is the number of subcarriers per RB. To support multiple UEs, multiple DMRSs are generated based on a single Zadoff-Chu [88] core sequence or a computer generated constant amplitude zero autocorrelation (CG-CAZAC) sequence by cyclic shifting of the core sequence. The main sequences are divided into 30 groups, and neighboring LTE cells select DMRS from different groups to reduce inter-cell interference. For example, if the maximum number of resource blocks within one OFDM symbol is 110 (i.e., assuming a total signal bandwidth of 20 MHz), then it is possible to generate a maximum of 110 x 30 = 3300 different sequences.

In one embodiment of the present invention, the DIDO system assigns UEs to "virtual cells" to provide the maximum number of SRS or DMRS that can be applied in the UL. In one embodiment, a virtual cell is a coherence region (described in related co-pending US Patent Application Ser. No. 13/232,996 entitled "Systems and Methods for Using Coherence Regions in Wireless Systems") around a UE, and the DIDO system generates maximum 3300 coherence regions for different UEs. In another embodiment of the present invention, each of the 30 master sequences is assigned to different DIDO clusters (Clusters are defined in related U.S. Patent No. 8,170,081, issued May 1, 2012, entitled "System and method for adjusting interference suppression in DIDO systems based on signal strength measurements" ) to reduce inter-cluster interference across adjacent DIDO clusters. In another embodiment, SRS or DMRS are assigned in accordance with certain frequency hopping models to use frequency channel diversity.

In the event that orthogonal SRS or DMRS are not sufficient to simultaneously serve all UEs in DL through DIDO precoding, one alternative is to multiplex SRS or DMRS of different UEs in the time domain. For example, the UEs are divided into different groups, and the SRS or DMRS for these groups are sent in consecutive time slots (0.5 ms each). However, in this case, it is necessary to ensure that the periodicity of assigning SRS or DMRS to different groups is lower than the channel coherence time for the fastest moving UE. In fact, a necessary condition is to ensure that the channel for all UEs does not change from the time the CSI is estimated by SRS or DMRS until the system transmits data streams over DL to the UE by DIDO precoding. In one embodiment of the present invention, the system divides active UEs into groups and assigns the same set of SRSs or DMRSs to each group in consecutive timeslots. In the same embodiment, the system estimates the shortest channel coherence time for all active UEs and calculates the maximum number of UE groups as well as the SRS or DMRS time multiplexing frequency based on this information.

3. DIDO Uplink Transmission Techniques in LTE

Embodiments of the present invention use UL open-loop MU-MIMO schemes to obtain simultaneous UL data streams from all UEs on a BTS. One embodiment of the UL open loop MU-MIMO scheme includes the following steps: i) UEs 1-4 send signaling information and payload to all BTSs 903; ii) BTS 903 calculate channel estimates from all UEs using the signaling information; iii) BTS 903 send channel estimates and payload to CP 901; iv) The CP 901 applies channel estimates to eliminate inter-channel payload interference from all UEs through spatial filtering and demodulates the data streams from all UEs. In one embodiment, an open-loop MU-MIMO system uses single carrier frequency division multiple access (SC-FDMA) to increase the number of UL channels from the UE to the BTS and multiplexes them in the frequency domain.

In one embodiment, synchronization among UEs is achieved by sending signals from the DL and it is assumed that all BTS 903 are connected to the same time/frequency reference clock in one embodiment by GPSDO or by direct wire connection to the same volume. same generator, or by sharing a common time/frequency reference. Channel delay variations propagated to different UEs can generate variability among different UEs' timing references, which can affect the performance of UL MU-MIMO methods. In one embodiment, only UEs within the same DIDO cluster (eg, UEs located in close proximity to each other) are processed by MU-MIMO techniques to reduce relative propagation delay across different UEs. In another embodiment, relative propagation delays between UEs are compensated at the UE or at the BTS to ensure that payloads from different UEs 1-4 are received simultaneously at the BTS 903.

The techniques for providing signaling information for data demodulation over UL may be the same as those used for signaling on the downlinks in the open loop DIDO scheme described in the previous section. The CP 901 may use different spatial processing techniques to eliminate inter-channel interference from the UE payload. In one embodiment of the present invention, the CP 901 uses non-linear spatial processing techniques such as maximum likelihood (ML) receivers, decision feedback equalization (DFE), or successive interference cancellation (SIC) receivers. In another embodiment, the CP 901 uses line filters, such as Zero Zeroing (ZF) or Minimum Mean Square Error (MMSE) receivers, to eliminate inter-channel interference and individual upstream demodulation.

4. Integration with existing LTE networks

In the United States of America and other regions of the world, LTE networks are already operational or in the process of being deployed, and/or a decision has been made to deploy them. For LTE operators, it will be a significant benefit to ensure that DIDO capabilities are gradually introduced into existing deployments or into deployments that have been decided upon. In this way, they will be able to deploy DIDO in the areas where they will get the fastest benefit, and gradually expand DIDO capabilities to cover a larger area of their network. Over time, with sufficient DIDO coverage in the region, they will be able to decide to completely phase out the use of cells, instead switching completely to DIDO and getting much higher spectral density at a much lower cost. During this full transition from cellular systems to DIDO, LTE wireless customers will experience no degradation in quality of service at all. On the contrary, they will experience an increase in data throughput and reliability, and the operator will see a reduction in their costs.

There are several options for implementation, which will ensure the gradual integration of DIDO into existing LTE networks. In all cases, BTSs for DIDO will be referred to as DIDO-LTE BTSs and will use one of the LTE compatible DIDO implementations described above or other LTE compatible implementations that may be developed in the future. Alternatively, DIDO-LTE BTSs will use a lightweight version of the LTE standard such as those described above and UEs will either be upgraded (e.g. if a software update is sufficient to modify the UEs to be DIDO compliant) or a new generation will be deployed. UE compatible with DIDO. In any case, new BTSs supporting DIDO either within the limitations of the LTE standard or as a variant of the LTE standard will be referred to below as DIDO-LTE Base Transceiver Stations (BTS).

The LTE standard supports various channel bandwidths (for example, 1.4, 3, 5, 10, 15, and 20 MHz). In one embodiment, an operator of an existing LTE network can either allocate new bandwidth to LTE-DIDO BTSs or split the existing LTE band (e.g., 20 MHz can be split into two 10 MHz blocks) to support regular LTE BTSs in a cellular configuration in one block. band and BTS DIDO-LTE in another band unit. In effect, this will create two separate LTE networks, and the UEs will be configured to operate on one network or the other, or to choose between the two networks. In the case of band subdivision, the band can be divided equally between the regular LTE network and the DIDO-LTE network, or unequally, with more band allocated to whichever network can make the best use of it given a given level of deployment of LTE cellular BTSs and DIDO-LTE BTSs and/ or UE application models. This subdivision can be changed over time as needed, and at some point, when enough DIDO-LTE BTSs have been deployed to provide the same or better coverage as provided by cellular BTSs, the entire range can be dedicated to DIDO-LTE BTSs, and cellular BTSs can be decommissioned.

In another embodiment, regular cellular LTE BTSs can be configured to coordinate with DIDO-LTE BTSs so that they can share the same band alternately. For example, with an equal amount of band sharing, each BTS will alternately use one 10ms frame, eg, one 10ms frame for an LTE cellular BTS and then one 10ms frame for a DIDO-LTE BTS. Frames can also be subdivided into unequal time intervals. This slicing can be changed over time as needed, and at some point, when enough DIDO-LTE BTSs have been deployed to provide the same or better coverage as provided by cellular BTSs, the entire range can be dedicated to DIDO-LTE BTSs. with the decommissioning of BTS.

In another embodiment of the present invention, DIDO is used as a LOS or NLOS wireless transport network for small cells in LTE and LTE-Advanced networks. When deploying small cells in LTE networks, the DIDO system provides them with a high-speed wireless backhaul network. As the demand for higher data rates grows, more and more small cells are added to the network until the wireless network reaches a limit where it is not possible to add small cells to it in a given area without causing inter-cell interference. In the same embodiment of the present invention, DIDO BTSs are used to gradually replace small cells, thereby increasing network capacity through inter-cell interference.

Links

[1] A. Paulraj, R. Nabar, and D. Gore, Introduction to Space-Time Wireless Communications, Cambridge University Press, 40 West 20th Street, New York, NY, USA, 2003

[2] D. Gesbert, M. Shafi, D. Shiu, P.J. Smith and A. Naguib, “From theory to practice: an overview of MIMO space-time coded wireless systems”, IEEE Journal on Selected Areas on Communications, vol.2, n.3, pp.281–302, Apr. 2003

[3] L. Zheng and D. N. C. Tse, “Diversity and multiplexing: a fundamental tradeoff in multiple-antenna channels,” IEEE Trans. Info. Th., vol. 49, no. 5, pp. 1073–1096, May 2003

[4] D. N. C. Tse, P. Viswanath, and L. Zheng, “Diversity-multiplexing tradeoff in multiple-access channels”, IEEE Trans. Info. Th., vol. 50, no. 9, pp. 1859–1874, Sept. 2004

[5] E. Visotsky and U. Madhow, “Space-time transmit precoding with imperfect feedback,” IEEE Trans. Info. Th., vol. 47, pp. 2632–2639, Sep. 2001.

[6] S. A. Jafar, S. Vishwanath, and A. Goldsmith, “Channel capacity and beamforming for multiple transmit and receive antennas with covariance feedback,” Proc. IEEE Int. Conf. on Comm., vol. 7, pp. 2266–2270 Jun. 2001.

[7] S. A. Jafar and A. Goldsmith, “Transmitter optimization and optimality of beamforming for multiple antenna systems,” IEEE Trans. Wireless Comm., vol. 3, pp. 1165–1175, July 2004.

[8] E. A. Jorswieck and H. Boche, “Channel capacity and capacity-range of beamforming in MIMO wireless systems under correlated fading with covariance feedback,” IEEE Trans. Wireless Comm., vol. 3, pp. 1543–1553, Sep. 2004.

[9] A. L. Moustakas and S. H. Simon, “Optimizing multiple-input single-output (MISO) communication systems with general Gaussian channels: nontrivial covariance and nonzero mean,” IEEE Trans. Info. Th., vol. 49, pp. 2770–2780, Oct. 2003.

[10] M. Kang and M. S. Alouini, “Water-filling capacity and beamforming performance of MIMO systems with covariance feedback,” IEEE Work. onSign. Proc. Adv. in Wire. Comm., pp. 556–560, June 2003.

[11] S. H. Simon and A. L. Moustakas, “Optimizing MIMO antenna systems with channel covariance feedback,” IEEE Jour. select. Areas in Comm., vol. 21, pp. 406–417, Apr. 2003.

[12] S. M. Alamouti, “A simple transmit diversity technique for wireless communications,” IEEE Jour. select. Areas in Comm., vol. 16, no. 8, pp. 1451–1458 Oct. 1998.

[13] V. Tarokh, N. Seshadri, and A. R. Calderbank, “Space-time codes for high data rate wireless communication: Performance criterion and code construction,” IEEE Trans. Info. Th., vol. 44, pp. 744-65, Mar. 1998.

[14] V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codes from orthogonal designs,” IEEE Trans. Info. Th., vol. 45, pp. 1456-467, July 1999.

[15] E. N. Onggosanusi, A. G. Dabak, and T. A. Schmidl, “High rate space-time block coded scheme: performance and improvement in correlated fading channels,” Proc. IEEE Wireless Comm. and Net. Conf., vol. 1, pp. 194-199, Mar. 2002.

[16] G. D. Durgin, Space-Time Wireless Channels, Prentice Hall, Upper Saddle River, NJ, USA, 2003

[17] D.-S. Shiu, G. J. Foschini, M. J. Gans, and J. M. Kahn, “Fading correlation and its effect on the capacity of multielement antenna systems,” IEEE Trans. Comm., vol. 48, no. 3, pp. 502-513, Mar. 2000

[18] A. Forenza and R. W. Heath Jr., “Impact of antenna geometry on MIMO communication in indoor clustered channels,” Proc. IEEE Antennas and Prop. Symp., vol. 2, pp. 1700-1703, June 2004.

[19] E. A. Jorswieck and H. Boche, “Channel capacity and capacity-range of beamforming in MIMO wireless systems under correlated fading with covariance feedback,” IEEE Trans. Wireless Comm., vol. 3, pp. 1543–1553, Sep. 2004

[20] R. W. Heath Jr. and A. Paulraj, “Switching between multiplexing and diversity based on constellation distance,” Proc. of Allerton Conf. on 208 Comm. Control and Comp., Sep. 2000.

[21] S. Catreux, V. Erceg, D. Gesbert, and R. W. Heath Jr., “Adaptive modulation and MIMO coding for broadband wireless data networks,” IEEE Comm. Mag., vol. 2, pp. 108–115, June 2002.

[22] A. Forenza, A. Pandharipande, H. Kim, and R. W. Heath Jr., “Adaptive MIMO transmission scheme: Exploiting the spatial selectivity of wireless channels,” Proc. IEEE Veh. Technol. Conf., vol. 5, pp. 3188–3192, May 2005

[23] C. B. Chae, A. Forenza, R. W. Heath, Jr., M. R. McKay, and I. B. Collings, “Adaptive MIMO Transmission Techniques for Broadband Wireless Communication Systems,” IEEE Communications Magazine, vol. 48, no. 5, pp. 112–118, May 2010

[24] FCC, “Broadband action agenda”, National Broadband Plan, 2010 http://www.broadband.gov/plan/national-broadband-plan-action-agenda.pdf

[25], N. Delfas, F. Meunier, S. Flannery, T. Tsusaka, E. Gelblum and S. Kovler, “Mobile data wave: who dares to invest, wins”, Morgan Stanley Research Global, June 13, 2012

[26] D. Goldman, “Sorry, America: your wireless airwaves are full”, CNN Money http://money.cnn.com/2012/02/21/technology/spectrum_crunch/index.htm

[27] P. Rysavy, “No silver bullets for FCC, NTIA spectrum challenge”, Daily report for executives, Bloomberg BNA, Aug. 2012 http://www.rysavy.com/Articles/2012_09_No_Spectrum_Silver_Bullets.pdf

[28] T. W. Hazlett, “Radio spectrum for a hungry wireless world”, Sept. 22, 2011

[29] B. J. Love, D. J. Love and J. V. Krogmeier, “Like deck chairs on the Titanic: why spectrum reallocation won’t avert the coming data crunch but technology might keep the wireless industry afloat”, Feb. 2012

[30] Qualcomm, “The 1000x data challenge, the latest on wireless, voice, services and chipset evolution”, 4G World, Oct. ^31st , 2012

[31] J. Lee, J.-K. Han, J. Zhang, “MIMO technologies in 3GPP LTE and LTE-advanced”, EURASIP Journal on Wireless Communications and Networking, Hindawi, May 2009

[32] 3GPP, TS 36.201, “Evolved Universal Terrestrial Radio Access (E-UTRA); LTE Physical Layer-General Description (Release 8)”

[33] 3GPP, TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”

[34] 3GPP, TS 36.212, “Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 8)”

[35] 3GPP, TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 8)”

[36] T. Yoo, N. Jindal, and A. Goldsmith, “Multi-antenna broadcast channels with limited feedback and user selection,” IEEE Journal on Sel. Areas in Communications, vol. 25, pp. 1478–91, July 2007.

[37] P. Ding, D. J. Love, and M. D. Zoltowski, “On the sum rate of channel subspace feedback for multi-antenna broadcast channels,” in Proc., IEEE Globecom, vol. 5, pp. 2699–2703, November 2005.

[38] N. Jindal, “MIMO broadcast channels with finite-rate feedback,” IEEE Trans. on Info. Theory, vol. 52, pp. 5045–60, November 2006.

[39] D. J. Love, R. W. Heath, Jr., V. K. N. Lau, D. Gesbert, B. D. Rao, and M. Andrews, “An Overview of Limited Feedback in Wireless Communication Systems,” IEEE Journal on Sel. Areas in Comm., Special Issue on Exploiting Limited Feedback in Tomorrow's Wireless Communication Networks, vol. 26, no. 8, pp. 1341–1365 Oct. 2008.

R. W. Heath, Jr., D. J. Love, V. K. N. Lau, D. Gesbert, B. D. Rao, and M. Andrews, “Exploiting Limited Feedback in Tomorrow's Wireless Communication Networks,” IEEE Journal on Sel. Areas in Comm., Special Issue on Exploiting Limited Feedback in Tomorrow's Wireless Communication Networks, vol. 26, no. 8, pp. 1337–1340 Oct. 2008.

[41] D. J. Love, R. W. Heath, Jr., and T. Strohmer, “Grassmannian Beamforming for Multiple-Input Multiple-Output Wireless Systems,” IEEE Trans. on Info. Theory special issue on MIMO Communication, vol. 49, pp. 2735–2747, Oct. 2003

[42] C. B. Chae, D. Mazzarese, N. Jindal and R. W. Heath, Jr., “Coordinated Beamforming with Limited Feedback in the MIMO Broadcast Channel” IEEE Journal on Sel. Areas in Comm., Special Issue on Exploiting Limited Feedback in Tomorrow's Wireless Communication Networks, vol. 26, no. 8, pp. 1505–1515 Oct. 2008

[43] A. Paulraj, “Is OFDMA, MIMO and OS the right stuff for mobile broadband?” http://www.ieeevtc.org/vtc2005fall/presentations/paulraj.pdf, Sept. 2005

[44] J. Wannstrom, “Carrier aggregation explained”, 3GPP

[45] 3GPP, TS 36.808, “Evolved Universal Terrestrial Radio Access (E-UTRA); Carrier Aggregation (Release 10)”, v10.0.0, June 2012

[46] Nokia Siemens Networks, “2020: beyond 4G, radio evolution for the gigabit experience”, White Paper, 2011, www.nokiasiemensnetworks.com

[47] S. Marek, “AT&T's Rinne talks about carrier aggregation trials, small cells and more”, http://www.fiercebroadbandwireless.com/story/atts-rinne-talks-about-carrier-aggregation-trials-small- cells-and-more/2012-11-08

[48] M. Reed, InterfereX, Tech23, 2011

[49] NICTA, “InterfereX”,

[50] J. Duplicity, et al., “MU-MIMO in LTE systems”, EURASIP Journal on Wireless Communications and Networking, Mar. 2011

[51] S. Feng and E. Seidel, “Self-organizing networks (SON) in 3GPP LTE”, Nomor research, May 2008

[52] NEC, “Self organizing networks,” White paper, Feb. 2009

[53] U.S. Patent No. 5,809,422, issued September 15, 1998, entitled “Distributed microcellular communications system”, G. R. Raleigh, M. A. Pollack

[54] G. J. Foschini, H. C. Huang, K. Karakayali, R. A. Valenzuela, and S. Venkatesan. The Value of Coherent Base Station Coordination. In Conference on Information Sciences and Systems (CISS 2005), Mar. 2005

[55] M. K. Karakayali, G. J. Foschini, R. A. Valenzuela, and R. D. Yates, “On the maximum common rate achievable in a coordinated network,” Proc. of the Int'l Conf. on Communications (ICC'06), vol. 9, pp. 4333–4338, June 2006.

[56] M. K. Karakayali, G. J. Foschini, and R. A. Valenzuela, “Network coordination for spectrally efficient communications in cellular systems,” IEEE Wireless Communications Magazine, vol. 13, no. 4, pp. 56–61, Aug. 2006.

[57] G. J. Foschini, M. K. Karakayali, and R. A. Valenzuela, “Coordinating multiple antenna cellular networks to achieve enormous spectral efficiency,” Proceedings of the IEEE, vol. 153, no. 4, pp. 548–555, Aug. 2006.

[58] S. Venkatesan, A. Lozano, and R. Valenzuela, “Network MIMO: overcoming inter-cell interference in indoor wireless systems”, Proc. of Asilomar conf., pp.83–87, Nov. 2007

[59] S. Venkatesan, H. Huang, A. Lozano, and R. Valenzuela, “A WiMAX-based implementation of network MIMO for indoor wireless systems”, EURASIP Journal on Advances in Signal Processing, Sep. 2009

[60] Y. Liang, R. Valenzuela, G. Foschini, D. Chizhik, and A. Goldsmith, “Interference suppression in wireless cellular networks through picocells”, ACSSC, pp.1041–1045, Nov. 2007

[61] A. Papadogiannis, H. J. Bang, D. Gesbert, and E. Hardouin, “Efficient selective feedback design for multicell cooperative networks”, IEEE Trans. On Vehicular Techn., pp.196–205, vol.60, n.1, Jan. 2011

[62] I. F. Akyildiz, D. M. Guterrez-Estevez, E. C. Reyes, “The evolution to 4G cellular systems: LTE-Advanced”, Physical communication, Elsevier, pp.217–244, 2010

[63] A. Barbieri, P. Gaal, S. Geirhofer, T. Ji, D. Malladi, Y. Wei, and F. Xue, “Coordinated downlink multi-point communications in heterogeneous cellular networks”, (Qualcomm), Information Theory and App. Workshop, pp. Feb. 7-16 2012

[64] S. Parkvall, E. Dahlman, A. Furuskar, Y. Jading, M. Olsson, S. Wanstedt, and K. Zangi, “LTE-Advanced — evolving LTE towards IMT-Advanced”, (Ericsson) IEEE VTC , pp.1–5, Sep. 2008

[65] R. A. Monziano and T. W. Miller, Introduction to Adaptive Arrays, New York: Wiley, 1980.

[66] K. K. Wong, R. D. Murch, and K. B. Letaief, “A jointchannel diagonalization for multiuser MIMO antenna systems,” IEEE Trans. Wireless Comm., vol. 2, pp. 773–786, Jul 2003;

[67] R. Chen, R. W. Heath, Jr., and J. G. Andrews, “Transmit Selection Diversity for Unitary Precoded Multiuser Spatial Multiplexing Systems with Linear Receivers,”' IEEE Trans. on Signal Proc., vol. 55, no. 3, pp. 1159-1171, Mar. 2007.

[68] M. Costa, “Writing on dirty paper,” IEEE Transactions on Information Theory, Vol. 29, no. 3, Page(s): 439–441, May 1983.

[69] G. Caire and S. Shamai, “On the achievable throughput of a multiantenna Gaussian broadcast channel,” IEEE Trans. Info.Th., vol. 49, pp. 1691-1706, July 2003.

[70] Nihar Jindal & Andrea Goldsmith, “Dirty Paper Coding vs. TDMA for MIMO Broadcast Channels”, IEEE Trans. on Info. Theory, vol.51, pp.1783–1794, May 2005

[71] M. Tomlinson, “New automatic equalizer employing modulo arithmetic,” Electronics Letters, Page(s): 138–139, March 1971.

[72] H. Miyakawa and H. Harashima, “A method of code conversion for digital communication channels with intersymbol interference,” Transactions of the Institute of Electronic

[73] U. Erez, S. Shamai (Shitz), and R. Zamir, “Capacity and lattice-strategies for cancelling known interference,” Proceedings of International Symposium on Information Theory, Honolulu, Hawaii, Nov. 2000.

[74] W. Yu and J. M. Cioffi, “Trellis Precoding for the Broadcast Channel”, IEEE Globecom, vol.2, pp.1344–1348, 2001

[75] B. M. Hochwald, C. B. Peel, and A. L. Swindlehurst, “A Vector-Perturbation Technique for Near-Capacity Multiantenna Multiuser Communication—Part I: Channel Inversion and Regularization”, IEEE Trans. On Communications, vol. 53, n.1, pp.195–202, Jan. 2005

[76] B. M. Hochwald, C. B. Peel, and A. L. Swindlehurst, “A Vector-Perturbation Technique for Near-Capacity Multiantenna Multiuser Communication—Part II: Perturbation”, IEEE Trans. On Communications, vol. 53, no. 3, pp.537–544, Mar. 2005

[77] S. Perlman and A. Forenza, “Distributed-input distributed-output (DIDO) wireless technology: a new approach to multiuser wireless”, Rearden Labs White Paper, July 2011, http://www.reardenwireless.com/ 110727-DIDO-A%20New%20Approach%20to%20Multiuser%20Wireless.pdf

[78] A. Vance, “Steve Perlman’s wireless fix”, Businessweek, July 2011 http://www.businessweek.com/magazine/the-edison-of-silicon-valley-07272011.html

[79] M. Lindström (Ericsson), “LTE-Advanced Radio Layer 2 and RRC aspects”, 3GPP TSG-RAN WG2

[80] Anritsu, “LTE resource guide”, www.us.anritsu.com

[81] 3GPP, “Spatial Channel Model AHG (Combined ad-hoc from 3GPP & 3GPP2)”, SCM Text V6.0, April 22, 2003

[82] J. Lee, “Introduction of LTE-Advanced DL/UL MIMO”, Samsung Electronics, Sep. 2009

[83] E. Dahlman, S. Parkvall and J. Skold, “4G: LTE/LTE-Advanced for mobile broadband”, Elsevier, 2011.

[84] J. Syren, “Overview on the 3GPP long term evolution physical layer”, Freescale White Paper, July 2007

[85] M. Baker, “LTE-Advanced physical layer”, Alcatel-Lucent, Dec. 2009

[86] J. Xu, “LTE-Advanced signal generation and measurements using SystemVue”, Agilent Technologies

[87] X. Hou and H. Kayama, “Demodulation reference signal design and channel estimation for LTE-Advanced uplink”, DOCOMO, Adv. in Vehic. netw. Tech., Apr. 2011

[88] D.C. Chu, “Polyphase codes with good periodic correlation properties”, IEEE Trans. Info. Theory, vol. 18, no. 4, pp. 531–532, July 1972

Claims (50)

1. A multi-antenna system (MAS) with multiple user (MU) transmissions ("MU-MAS") for wireless communications, comprising: many user devices; a plurality of distributed antennas or wireless transceivers and one or a plurality of centralized processing units (CPs); wherein at least one transceiver uses radio frequency (RF) calibration to convert uplink (UL) channel state information (CSI) to downlink (DL) CSI, and at least one CP uses CSI to calculate a set of weights precoding coefficients, generates a plurality of shaped signals, and sends or receives a plurality of shaped signals that intentionally interfere to create a plurality of matching non-interfering data links with user devices within the same frequency band. 2. The system of claim 1, wherein the power transmitted from the plurality of antennas is limited to minimize interference at cell boundaries, and spatial processing is used to eliminate inter-cell interference. 3. The system of claim 1, wherein the power transmitted from the plurality of antennas is not limited to any particular power level, so that inter-cell interference is deliberately created throughout the cell and used to increase the capacity of the wireless communication network. 4. The system of claim 1, wherein the wireless communications network is a cellular network, such as a Long Term Evolution (LTE) network. 5. The system according to claim. 1, in which the wireless communication network is a distributed system of antennas with access points placed intuitively without restrictions on the transmitted power to prevent inter-cell interference. 6. The system of claim 1, comprising one or more base transceiver station (BTS) units and one or more user equipment (UE) units. 7. The system of claim 1, wherein the precoding methods for closed loop systems are used to send simultaneous non-interfering data streams from the BTS to the UE on a downlink (DL) channel. 8. The system of claim 7, wherein each UE applies a cell specific reference signal (CRS) to estimate channel state information (CSI) from all BTSs or only from BTSs within its own user cluster, the user cluster being defined as a plurality of BTSs. available from the location of the UE. 9. The system of claim 8, wherein the CP estimates channel time and frequency selectivity and dynamically re-allocates CRS to different BTSs for different resource elements. 10. The system of claim 7, wherein each UE applies a channel state information reference signal (CSI-RS) or a demodulation reference signal (DM-RS) or a combination of both to estimate CSI from all BTSs or only from BTSs within its own user cluster. 11. The system of claim 10, wherein the transmit power from the BTS is reduced so that the number of BTSs in the user cluster is below the maximum number of antennas supported by the CSI-RS scheme in the LTE standard. 12. The system of claim 10, wherein the BTSs within the user cluster are divided into subsets and the CSI-RS is sent from one subset of BTSs at a time at a predetermined frequency. 13. The system of claim 12, wherein the periodicity of the CSI-RS for different subsets is determined based on the channel coherence time of the UE as well as the periodicity supported by the LTE standard. 14. The system of claim 10, wherein the CSI-RS is allowed different periodicity models and values than those provided in the LTE standard to provide more BTSs in the system. 15. The system of claim 7, wherein the UE transmits a rank index (RI), a precoding matrix index (PMI), and a channel quality index (CQI) to the CP via an uplink physical control channel (PUCCH). 16. The system of claim 7, wherein the UE transmits RI, PMI, and CQI to the CP via a common uplink physical channel (PUSCH). 17. The system of claim 16, wherein the system estimates channel frequency selectivity and dynamically adjusts the PMI to support more BTSs for the same available uplink (UL) resource. 18. The system of claim 1, wherein the precoding methods for open loop systems are used to send simultaneous non-interfering data streams from the BTS to the UE over a DL channel. 19. The system of claim. 1, in which the methods for systems without feedback are used to receive simultaneous non-interfering data streams from the UE to the BTS over the UL channel. 20. The system of claim 18, wherein a sounding reference signal (SRS) or DMRS is applied to estimate the channel impulse response from all UEs to the BTS. 21. The system of claim 20, wherein different SRSs or DMRSs are assigned to different antennas of each UE. 22. The system of claim 20, wherein different SRSs or DMRSs are assigned to different subsets of BTSs to reduce interference between non-interacting BTSs. 23. The system of claim 20, wherein SRS or DMRS are assigned based on frequency hopping models to use frequency channel diversity. 24. The system of claim 20, wherein the active UEs are divided into groups such that the same set of SRSs or DMRSs is assigned to each group in consecutive timeslots. 25. The system of claim 24, wherein the shortest channel coherence time for all active UEs is estimated, and based on this information, the number of UE groups as well as the periodicity of the SRS or DMRS time multiplexing scheme is calculated. 26. The system of claim 19, wherein time and frequency synchronization among UEs is achieved by using DL signaling information. 27. The system of claim 26, wherein the BTSs are synchronized to the same reference clock by direct wiring to the same physical clock, or by sharing a common time and frequency reference with system-disciplined oscillators. global positioning (GPSDO). 28. The system of claim 26, wherein relative propagation delays between UEs are prevented by processing UL frames only for those UEs associated with the same set of BTSs, thereby guaranteeing time synchronization between UEs. 29. The system of claim 26, wherein the relative propagation delays between UEs are pre-compensated at the UE side prior to transmission on the UL, which guarantees UE timing at the BTS receivers. 30. The system of claim 19, wherein the open-loop methods comprise non-linear spatial filters such as maximum likelihood (ML), decision feedback compensation (DFE), or successive interference cancellation (SIC) receivers. 31. The system of claim 19, wherein the open-loop methods comprise linear spatial filters, such as zero-to-zero (ZF) or minimum mean square error (MMSE) receivers. 32. The system of claim 19, wherein SC-FMDA is used for frequency domain multiplexing of the UE. 33. The system of claim. 1, in which MU-MAS technology is gradually integrated into existing LTE networks. 34. The system of claim. 1, in which the BTS or UE is compatible with LTE. 35. The system of claim. 1, in which the BTS and/or UE uses a variant of the LTE standard. 36. The system of claim 1, wherein the LTE UEs are updated to be compatible with MU-MAS technology. 37. The system of claim 35 wherein a new generation of MU-MAS compatible UEs is deployed. 38. The system of claim 1, wherein the LTE band is subdivided to support regular LTE BTSs in a cellular configuration in one band block and MU-MAS LTE BTSs in another band block. 39. The system according to claim 1, in which conventional cellular LTE BTSs are configured to coordinate with MU-MAS LTE BTSs in such a way that they share the same band, but operate in accordance with time division multiple access schemes ( TDMA). 40. The system of claim 1, wherein the MU-MAS is used as a line of sight (LOS) or non-line of sight (NLOS) wireless transport network for LTE small cells. 41. The system of claim 1, wherein the LTE small cells are gradually replaced by MU-MAS BTSs. 42. The system of claim 18, wherein RF calibration is applied to convert CSI UL to CSI DL, thus using the UL/DL channel reciprocity principle. 43. The system of claim 19, wherein a sounding reference signal (SRS) or DMRS is applied to estimate the channel impulse response from all UEs to the BTS. 44. A wireless communication method implemented within a multi-antenna system (MAS) with multiple user (MU) transmissions ("MU-MAS"), including: many user devices; a plurality of distributed antennas or wireless transceivers and one or a plurality of centralized processing units (CPs); wherein at least one transceiver uses radio frequency (RF) calibration to convert uplink (UL) channel state information (CSI) to downlink (DL) CSI, and at least one CP uses CSI to calculate a set of weights precoding coefficients, generates a plurality of shaped signals, and sends or receives a plurality of shaped signals that intentionally interfere to create a plurality of matching non-interfering data links with user devices within the same frequency band.

Images