Forward error correction scheme in a wireless system

The present invention relates to a low latency error correction mechanism and to a high data transmission rate over multiple traffic channels within a wireless communication system.

WO 99/14878 A1 and WO 98/43373 A1 disclose the closest technique.

It is known to include forward error correction coding (FEC) and decoding on information signals to be transmitted over a wireless channel. Forward-looking error correction generally introduces predetermined redundancy into an information signal to enable a receiver to identify and possibly correct errors that may have been applied from a transmission medium. The known IS-95 standard for code division cellular multiple access communication specifies e.g. a type of envelope code for each traffic channel used for transmission from a base station to a mobile station or vice versa.

More recently, it has been suggested to provide high-speed data exchange over an ice wireless communications facility. Such high-speed data exchange can e.g. is used to facilitate data transfer for data processing applications or for video conferencing applications. Within such a proposed scheme, a high data rate signal may be communicated to a receiver over multiple parallel traffic channels. The newly proposed IS-95 B standard, for example, proposes use of parallel CDMA channels each having a data rate of 9.6 KB / s to create high data rate communication. Within such equipment, a high data rate signal is demultiplexed to several lower data rate data signals, and each of these signals is then processed in an independent traffic channel. At each of these data signals with lower data rate, FEC has then been applied.

Another example of a wireless CDMA system that uses multiple parallel traffic channels for high-speed data exchange can be found in the co-pending patent application entitled Protocol Conversion and Bandwidth Reduction Technique Providing Multiple nB + D ISDN Basic Rate Interface Links to a Wireless Code Division Multiple Access Communication System, with serial no. 09 / 030,049, filed February 24, 1998, the contents of which are incorporated herein by reference.

Wireless communication channels have an inherent tendency to be noisy because of. Channel disturbances caused by atmospheric conditions, multipath effects, inter-channel interference, etc. Especially if the transmission is used for data processing applications, where execution instructions can be expected to be exchanged over traffic channels, the need for efficient FEC technology will still be important.

The use of more efficient FEC techniques in such wireless transmission systems can then increase the latency of data orders. The known turbo codes require e.g. reception of large data blocks solely by a decoder before the decoding can begin. The latency generally applies to the time delay running from the time a data order is sent out by a user and to the time when data in accordance with that order is available to the user. FEC introduces decoding delays into a wireless receiver and thus contributes to latency.

There is a need in the field of wireless communication equipment that will be able to perform high-speed data exchange with high-quality FEC, as well as with low latency.

SUMMARY

Embodiments of the present invention create a transmitter / receiver system for high data rate data transmission within a wireless communication system where a physical ice processor includes a FEC encoder, a demultiplexer, and several modem processors. The FEC encoder applies error correction codes to the high data rate signal. Then, the demultiplexer distributes portions of the high data rate encoded signal on the modem processors. Each modem processor processes its assigned portion of the encoded signal for transmission over its own channel.

The main features of the invention are set forth in the independent claims. Further features of the invention are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached figure shows a transmitter and a receiver, each of which is made in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

The present invention relates to low latency forward error correction for high data rate wireless transmission by applying forward error correction codes to that data prior to multiplexing data distributed over multiple fixed bandwidth parallel traffic channels.

The attached figure is a block diagram of a transmitter 100 and a receiver 200 each constructed in accordance with the embodiment of the present invention. The transmitter 100 and receiver 200 are shown for operation in a layered communication system comprising a transmission layer 110, 210, a physical layer 120, 220, and higher communication layers, such as network layers & data transfer layers (collectively designated 130 & 230). As will be known, a transmitter 100 in the transmission layer 110 performs carrier modulation, amplification, and transmission of data signals to be transmitted. As will also be known, a receiver 200 in the transmission layer 210 performs reception, amplification, and carrier demodulation to derive a recovered digital data signal. The higher layers 110,

io Iht. one embodiment of the present invention, the physical layer 120 of the transmitter 100 may include an FEC encoder 122, a demultiplexer 124, and a plurality of modem processors 126a-126n. The number of modem processors 126a-126n may vary and may also be determined from the amount of data to be transmitted and the transmission capacity of each of the traffic channels over which that data may be transmitted. The FEC encoder 120 is receiving a source signal from a higher layer 110 in the transmitter and enriching this signal with an error correction code. The enriched information signal Is is output from the FEC encoder 122 to the demultiplexer 124. The multiplexer distributes this information signal to the modem processors 126a-126n. These modem processors 126a-126n each form a respective portion of the enriched signal transmission signal.

In the receiver 200, the physical layer 220 performs the data processing which is the inverse of the processing applied to the physical layer 120 of the transmitter 100. This physical layer 220 may include a FEC decoder 222, a demultiplexer 224, and a plurality of demodulators 226a 226n. There will then be a demodulator 226a-226n for each of the traffic channels that has been allocated to convey the information signal. The recovered digital signal from the transmission layer 230 constitutes the input signal to each of the demodulators 226a-226n. Each demodulator 226a-226n emits a recovered portion of the information signal. The demultiplexer 224 combines each of the recovered portions of the information signal into a uniformly recovered information signal.

In a CDMA embodiment shown in the figure, a receiver 200 does not need to include an element corresponding to the adder 128 in the transmitter 100, the demodulators 226a-226n each performing correlation. As will be known, correlation allows a modem processor to discriminate a desired CDMA signal from others

CDMA signals that may be present in an aggregated received signal. Thus, in the embodiment shown in the figure, the demodulators 226a-226n can identify and output each respective respective portion of the recovered enriched information signal.

Acc. In a particular embodiment of the present invention, the FEC encoder 122 and the FEC decoder 222 can be generate and decode repeatedly systematically stacked codes, which will also be known as turbo codes. These turbo codes provide an advantage in that the FEC decoding process can be repeated several times to improve the information signal recovered from the decoding process. Thus, if the output of a first repetition can be reintroduced into the FEC decoding block (the path not shown in the figure) for subsequent repetitions. Acc. its kind generates the turbo codes improved corrected data ice for each subsequent repetition.

The known turbo codes, however, introduce a predetermined degree of latency into the decoding process. Turbo codes work on blocks of predetermined size. A turbo code intended for a wireless communication system to be used in connection with computer networks includes e.g. a block size of 4,096 channel 20 symbols. An FEC decoder 222 must decode a block in its entirety before a recovered information signal becomes available to the block. This feature may be in contrast to enveloped codes used in accordance with the present invention. the known IS-95 standard for CDMA cellular communication, with convoluted codes being characterized by relatively low latency for a block of the same size (relative to turbo codes), because then it will not be necessary to receive a block in its entirety before decoding can begin.

For use with high data rate and use of parallel traffic channels, it is then assumed that the use of turbo codes makes it possible to obtain a higher quality number (lower Eb / N₀ than for convoluted codes). Use of the example with a block of 4,096 channel symbols and E_b/ N₀ at 1.5 dB, then the turbo code will have a BER value of 10⁶ For voice systems that require a smaller string BER value of 10³, vil en konvolveringskode kreve en E_b/ N₀ of 7 dB or more.

The technique according to. The present invention finds application in many different wireless communication systems, including CDMA systems. In practice, the base stations and the subscriber stations in the wireless communication system will usually include the functionality of both the transmitter and the receiver in the figure. That is, to create bidirectional communication, a base station must include a transmitter portion 100 and a receiver portion 200. This will also be the case with the subscriber terminal. However, the base stations and the subscriber terminals need not be configured to provide simultaneous complete duplex communication.

Typically, a base station in a wireless communication facility will transmit multiple io data signals to many different subscribers simultaneously. Acc. In some embodiments of the present invention, each base station can then perform the processes set forth herein simultaneously on a plurality of high transmission rate data signals. It is then in accordance with the inventive content and scope of the present invention that each signal may have a data rate independent of the data rates of the other signals. In such a case, a base station may be configured to include its FEC encoder / decoder 122, 222 as well as modem processor / demodulators 126a, 226a, a merged configuration. Such an embodiment then makes it possible for the base station e.g. assigning a varying number of modem processors 126a-126n to a data signal according to the data rate or data rate of the signal to be transmitted. Similarly, include a compound unit of

FEC encoders 122 (shown individually in FIG. 1) in a base station, this base station will selectively enable FEC encoders 122 as the base station receives new data signals to be transmitted to subscribers. Creation of a base station comprising components of a summarized arrangement will be well known.

Several embodiments of the present invention are then specifically shown and described herein.

However, it will be appreciated that modifications and variations of the present invention will be covered by the foregoing disclosure and fall within the scope of the appended claims without departing from the spirit of the invention and intended scope.