HK1030116B - Channel coding and interleaving for transmissions on a multicarrier system - Google Patents

Description

Channel coding and insertion for transmission over multi-carrier systems

Technical Field

The present invention relates generally to transmitting and receiving data in a telecommunications system, and more particularly, to a system and method for encoding and inserting data into separate channels for transmission in a multi-carrier system.

Background

Generally, a wireless telecommunication system serves a defined area by dividing an area into cells. Each cell is served by a separate base station, or cell site, and each cell site is connected to a message switching center ("MSC") by appropriate hardwired communication lines. A mobile unit is connected to the MSC by establishing communication links with a nearby cell site using one or more radio frequency ("RF") channels, or carriers.

Higher data rates in RF communication lines between mobile units and cell sites are desirable for a variety of reasons. For example, in a code division multiple access ("CDMA") system, the data rate is somewhat limited by current standards that require a system bandwidth of 1.25 Megahertz (MHZ). However, future requirements will be extended to support system bandwidth n x 1.25MHZ, where n is an integer, to support compatibility with conventional 1.25MHZ bandwidth in the downward direction.

Once the system bandwidth n x 1.25MHZ is selected, there are two ways in which data can be transmitted over the selected bandwidth. One method, called direct spread spectrum, encodes the data using a convolutional code and inserts the resulting encoded bit stream, encodes the inserted symbols using a Walsh code unique to the user, further encodes the encoded symbols using a Pseudo Noise (PN) code, and then spreads the entire 1.25MHZ bandwidth. Using this method, the actual symbol rate on the RF carrier is n × 1.25 mega-chips/second. Another method, known as multi-carrier, divides the encoded data into n streams, encodes each stream with Walsh and PN codes, and then transmits the resulting chips for each stream on a respective 1.25MHZ carrier. A CDMA compatible standard for a cellular mobile telecommunications system including more details of the method described above, described below: mobile STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-mode wideband SPREAD SPECTRUM CELLULAR SYSTEMs (MOBILE STATION COMPATIONS FOR DUAL MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEM), TIA/EIA/IS-95(JULY 1993).

The multi-carrier approach described above is not suitable for handling error conditions that arise on separate carriers. For example, if several bit errors occur in the sequential order, the presence of error correction codes in the bit stream does not prevent some data bits from being lost. To alleviate this problem, the multi-carrier approach inserts data bits separately on each carrier before transmission, or scrambles the order of the data bits and then inserts the data bits at the receiving end, however, this solution has some disadvantages. First, a jammer circuit is typically used for each carrier, thereby requiring additional circuitry. Moreover, scrambling does not take into account that some carrier frequencies are more robust at any particular time and therefore less error prone than others.

A method for multi-channel transmission is disclosed in EP0758168, wherein a matrix frame is employed. However, the disclosed method does not involve multicarrier frequencies.

Therefore, there is a need for a system and method of encoding and inserting data on individual carriers for transmission in a multi-carrier system.

Furthermore, there is a need for a system and method that does not require separate insertion circuits for each carrier of a multi-carrier system.

Further, there is a need for a system and method that utilizes different carriers for successive bits of an error correction code, thus providing a versatile system that is less susceptible to errors.

Summary of The Invention

The above problems are solved and a technical advance is achieved by a system and method for encoding and inserting data into separate channels for transmission in a telecommunications system. In one embodiment, a multi-carrier telecommunications system has an input terminal for receiving data bits for a plurality of users. The system may add error correction bits to the user data bits. The system then arranges and stores combinations of error correction bits and the collectively encoded symbols in a two-dimensional matrix. The system arranges the symbols by writing them into the matrix column by column from left to right. The system then recovers the symbols from the matrix by rows from top to bottom and transmits the recovered symbols on different carrier frequencies such that each successive symbol is transmitted on a different carrier frequency.

As a result, the system reduces the impact of errors caused by any single carrier. Furthermore, the arrangement of the symbols is performed at a central location, thereby obviating the need for each carrier to have its own scrambling device.

Brief Description of Drawings

Fig. 1 is a block diagram of a base station and a mobile unit in a multi-carrier CDMA system.

Fig. 2 is a flow chart of a process for storing symbols received by the base station of fig. 1 in a matrix.

Fig. 3 is a flow chart of a process for recovering symbols stored in the matrix of fig. 2 for transmission.

Description of the preferred embodiments

Referring to fig. 1, reference numeral 10 designates a base station of a simplified multi-carrier CDMA system, the base station 10 comprising a convolutional encoder 12 (rate 1/m), a symbol repeater (K times) 14, and a block inserter 16 with a demultiplexer 16 a. The base station 10 uses at each frequency f₁-f_nA plurality of (n) carriers at each bandwidth of 1.25MHZ and each plus the usual Walsh codes 18.1-18.n and PN codes 20.1-20.n are processed (baseband filtered, upconverted, amplified) and transmitted by devices 21.1-21.n, respectively. For purposes of illustration, only the forward communication link from base station 10 to mobile unit 22 will be discussed, wherein a frame of 8 user data bits is received by the base station and transmitted as a stream of symbols divided into m × k × r blocks.

Each user data bit, when entering the convolutional encoder 12, is encoded as m symbols. The encoded symbols are then provided to a symbol repeater 14 where each symbol is repeated K times. The convolutional encoder 12 and the symbol repeater 14 are conventional devices for providing error correction capability and will not be discussed further for simplicity.

Referring to fig. 2, a method 50 is used to insert the symbol stream produced by the symbol repetition block 14. At step 52, the block inserter 16 composes a matrix of m × k × q rows and p columns, where q and p are positive integers and p × q ═ r. (1)

At step 54, the block inserter 16 writes the encoded symbols into the matrix, starting at the top of the first column and continuing down to the bottom of the first column, and once the first column is written, the symbols will fill the second column, from top to bottom. Step 54 is continued until all columns of the matrix are filled.

Referring to FIG. 3, once the matrix has been filled, a routine 70 is used to recover symbols from the matrix for use in recovering symbols from the matrixIn different carriers f₁-f_nAnd (4) transmitting. At step 72 the demultiplexer 16a recovers the first symbol on the first row and at step 74 sends the first symbol to the device 21.1 for on-carrier f₁And (4) sending. At step 76, the demultiplexer sequentially transmits the subsequent symbols on the first line for use on carrier f₂To f_nUp to one symbol on each carrier is transmitted on each of the n carriers. This step is repeated for several symbols up and down the first row until all symbols of the first row are transmitted. At step 78, a determination is made whether more rows are available. If not, execution stops. Otherwise, execution returns to step 72 where the demultiplexer 16a recovers the first symbol of the second row and sends this symbol to the device 21.2 for transmission on the carrier f, step 74₂And (4) sending. The demultiplexer then sends the following symbols on the second row for the carrier f₃，f₄，…f₁Transmitted until n symbols are transmitted on each of the n carriers. This is repeated for n symbols up and down the second row until all symbols on the second row are transmitted. If there are more rows, the demultiplexer 16a returns to step 72 to recover the first symbol of the third row on carrier f₃And sends the remaining symbols for use on carrier f₄，f₅…，f₄Send above, and so on. In row n +1, the demultiplexer 16a sends the carrier f to be present₁The first symbol transmitted, steps 72-78, are repeated. Likewise, the transmission line n +2, n + n +2, n + n + n +2, etc., each of the slave carriers f₂Initially, the remaining rows may be analogized.

For example, a frame of 10 user data bits (r-10) is encoded using a rate convolutional code of 1 to 3 (m-3), repeated twice (k-2), and then distributed among three different carrier signals (n-3). The resulting symbol stream is divided into blocks of 60 symbols and inserted with a crossover time and 3 carrier signals. A matrix shown in table 1 has 12 columns (q-12) and 5 rows (p-5), and each symbol of the matrix is denoted x_i，y_iOr z is_iTogether represent a convolution byEncoder 12 generates three bits from one bit of information, where i is between 1 and 10. Also, symbol x_i，y_iAnd z_iEach of which is repeated twice by the symbol repeater 14. With the method 50 described above, symbols are written into the columns of the matrix as follows: TABLE 1 insertion matrix

X1	Z1	Z2	Y3	Y4	X5	X6	Z6	Z7	Y8	Y9	X10
												X1	X2	Z2	Z3	Y4	Y5	X6	X7	Z7	Z8	Y9	Y10
Y1	X2	X3	Z3	Z4	Y5	Y6	X7	X8	Z8	Z9	Y10
												Y1	Y2	X3	X4	Z4	Z5	Y6	Y7	X8	X9	Z9	Z10
Z1	Y2	Y3	X4	X5	Z5	Z6	Y7	Y8	X9	X10	Z10

Once the symbols have been arranged in the matrix, the demultiplexer 16a recovers the symbols in the inserted fashion for the carrier f₁，f₂And f₃And (4) upward transmission. Traversing each row in the matrix of table 1 in order, the demultiplexer sends out each symbol to be transmitted in the order described in table 2 below. In Table 2, the column "NO" describes the order in which each symbol is sent, and the column "symbol" corresponds to that from Table 1The name, column "(RC)" flags the row and column of Table 1 where the symbol is stored, and the column "Rreq" flags the frequency at which the symbol is transmitted.

TABLE 2 Transmission sequence

No.	Symbol	(Row, column)	Frequency of
				1	X1	1，1	f1
2	Z1	1，2	f2
				3	Z2	1，3	f3
4	Y3	1，4	f1
				5	Y4	1，5	f2
6	X5	1，6	f3
				7	X6	1，7	f1
8	Z6	1，8	f2
				9	Z7	1，9	f3
10	Y6	1，10	f1
				11	Y9	1，11	f2
12	X10	1，12	f3
				13	X1	2，1	f2
14	X2	2，2	f3

No.	Symbol	(ranks)	Frequency of
				15	Z2	2，3	f1
16	Z3	2，4	f2
				17	Y4	2，5	f3
18	Y5	2，6	f1
				19	X6	2，7	f2
20	X7	2，8	f3
				21	Z7	2，9	f1
22	Z8	2，10	f2
				23	Y9	2，11	f3
24	Y10	2，12	f1
				25	Y1	3，1	f3
…	…	…	…
				59	X10	5，11	f2
60	Z10	5，12	f3

It will be appreciated that the mobile unit 22 has similar play characteristics as described above for the base station 10. Moreover, both the mobile unit 22 and the base station 10 also include receiver units for receiving and storing each symbol on the opposite line as described above, thereby enabling the data stream to be de-inserted and fully recovered.

In another embodiment, the block interpolator 16 may recover the symbols on the jth column and ith row of the matrix at the carrier frequency f_sIn the following way: m ═ (((j-1) × r + i-1) MODn) +1, (2)

Where r is the number of rows in the matrix, n is the number of carrier frequencies, 1 ≦ m ≦ n, and the function MOD represents the modulo operation. By using equation (2) above, the inserter 16 is assured that no two consecutive code symbols in the original code sequence are transmitted on the same carrier frequency.

Thus, while illustrative embodiments of the invention have been shown and described, other modifications, changes, and substitutions are contemplated in the foregoing disclosure. For example, convolutional encoder 12 may be left-handed, such that symbol repeater 14 provides the only source of error correction capability. Table 1 may also be arranged by rows, thereby enabling table 2 to recover symbols by columns. Furthermore, the present invention is not limited to cellular-based telecommunications systems, but may be used in many different types of systems, including wired transmission systems. It is appropriate, therefore, that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims (18)

1. In a telecommunications system having an input terminal for receiving a plurality of user data bits, an error correction device for generating a sequence of code symbols from the user data bits, and an inserter (16) for arranging and storing the code symbols in a matrix, the improvement comprising:

a demultiplexer (16a) for sequentially recovering the encoded symbols stored in the matrix and sequentially distributing the recovered encoded symbols over a plurality of carriers;

wherein the matrix is two-dimensional, the inserter (16) arranges the encoded symbols according to a first dimension, and the demultiplexer recovers the encoded symbols according to a second dimension.

2. The system of claim 1 further comprising a device (14) for repeating the encoded symbols.

3. The system of claim 1, wherein the error correction device comprises a repeater (14) and the sequence of code symbols comprises a replica of user data bits.

4. The system of claim 1, a wireless multi-carrier system, further comprising a code division multiple access ("CDMA") transmitter (21.1-21.n), one for each of the plurality of carriers.

5. The system of claim 4, wherein a plurality of sub-sequences of encoded symbols are generated for each user data bit, and successive symbols of a sub-sequence are transmitted on different carriers of the plurality of carriers.

6. The system of claim 2, wherein the repeated encoded symbols are transmitted sequentially on different carriers of the plurality of carriers.

7. The system of claim 1, wherein the error correction device provides forward error correction.

8. The system as claimed in claim 1, wherein each of the plurality of carriers operates over a common bandwidth.

9. The system of claim 1, wherein the system can selectively use one or more of the plurality of carriers.

10. A method for arranging successive bits of a frame for transmission in a multi-carrier system includes basing on a first dimension of a matrix. Arranging and storing each bit in the frame into a two-dimensional matrix and recovering each bit stored in the matrix according to a second dimension to form an inserted bit sequence, the improved method further comprising the steps of:

the interpolated bit sequence is transmitted using multiple carriers such that no two consecutive bits in the inserted bit sequence are transmitted on the same carrier.

11. The method of claim 10, wherein the first dimension represents multiple arrangements of bits and the plurality of carriers consecutively transmit bits in each arrangement.

12. The method of claim 10, wherein the step of transmitting uses a code division multiple access ("CDMA") transmitter (21.1-21.n) for each carrier in the multi-carrier system.

13. The method of claim 10, wherein the bit frame includes an error correction code.

14. The method of claim 13, wherein the bit frame also includes user data and the error correction code is a replica of the user data.

15. The method of claim 10, wherein each carrier in the multi-carrier system operates over a common bandwidth.

16. The method of claim 10, wherein the multi-carrier system utilizes only a single carrier.

17. A system for arranging bits of a frame for transmission in a multi-carrier wireless system having a means (16) for arranging and storing each bit of the frame in a two-dimensional matrix according to a first dimension of the matrix, the improvement comprising:

means (16a) for recovering each bit stored in the matrix according to a second dimension to form an inserted bit sequence; and

a code division multiple access transmitter (21.1-21.n) for transmitting an inserted sequence of bits, wherein the transmitting step utilizes multiple carriers operating over a common bandwidth and no two consecutive bits in the frame are transmitted on the same carrier;

wherein the first dimension represents a plurality of arrangements of the matrix and the first carrier transmits a first bit of the first arrangement and the second carrier transmits a first bit of the second arrangement.

18. The system of claim 17, wherein the bit frame includes an error correction code.