Signal detection in a TDMA system

Details Signal detection in a TDMA system Signal detection in a TDMA system

1997-04-07

1999-11-30

Pham, Chi H.

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

370347, 375349, H04B 7212

Patent

active

059954990

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a signal detection method in a receiver of a TDMA radio system, in which a primary signal and at least one interfering co-channel signal are received on the same TDMA channel, said signals having different but known training sequences and having different multipath propagation and thus different transmission channels on the radio path.
2. Description of Related Art
In future development of cellular mobile networks, the availability of the radio spectrum will be one of the key problems. In narrowband mobile systems, co-channel interference (CCI) is one of the main factors limiting system capacity. Conventionally, system capacity has been increased in this respect by increasing the geographical re-use of frequencies while decreasing cell size and transmission power. Of course, this is not the preferred manner, since the infrastructure may become intolerably expensive. Another possibility of solving the capacity problem is to follow the rapid development of digital signal processing and to utilize the rather complex interference cancelling algorithms. The removal of co-channel interference in a receiver enables a more efficient re-use of frequencies in a network.
In current mobile systems, co-channel signals are approximated as random additive white Gaussian noise in receivers. However, this approximation is sufficient only if interfering co-channel signals are sufficiently weak, which can be ensured by an appropriate degree of re-use of frequencies in a conventional cellular system. However, this is not the case in interference limited cellular systems. Actually, co-channel interference is typically deterministic in nature, which means that it should be possible to remove at least part of its influence.
Interference cancellation (IC) is already a popular issue in connection with code division multiple access systems (CDMA). Applying interference cancellation techniques to narrowband TDMA systems is, however, basically a more difficult task than in CDMA systems, where information on transmitted wave forms is available in advance in an interference cancelling receiver.
A radio transmitter signal usually undergoes so called multipath propagation, where the signal propagates along several different paths due to obstacles and reflections and arrives at a receiver as several signal components delayed in different ways. In digital systems, this so called time dispersion causes intersymbol interference (ISI), in which interference successive symbols are partly superimposed, which complicates demodulation in the receiver. In the pan-European mobile communications system GSM, a pre-known training sequence is included in a signal to be transmitted. This makes it is possible to estimate in a receiver the multipath channel via which the signal has travelled on the radio path. This estimated channel model allows the reciever to correct the received signal and to use the estimated channel model in the equalizer and demodulator of the receiver in the Viterbi algorithm. The GSM system specifies eight different training sequences in such a manner that it is possible to allocate different training sequences to channels using the same frequencies in cells which are sufficiently close to interfere with one another. A receiver can thus distinguish the correct signal from an interfering signal arriving at the same time. Since in a typical cellular system, such as the GSM, co-channel interference is kept, if possible, as low as possible by means of cellular network frequency planning, it is treated in a receiver merely as random Gaussian noise. Actual channel estimation, equalization and detection are performed without information on other co-channel signals. This does not cause problems in a correctly planned cellular network, where the distance between cells using the same channel is sufficiently long. However, if the utilization of a frequency band is to be increased by increasing the geographical re-use of frequencies in a cellular network,

REFERENCES:
patent: 4995104 (1991-02-01), Gitlin
patent: 5199047 (1993-03-01), Koch
patent: 5303226 (1994-04-01), Okanoue et al.
patent: 5373507 (1994-12-01), Skold
patent: 5533067 (1996-07-01), Jamal et al.
patent: 5596607 (1997-01-01), Larsson et al.
patent: 5768254 (1998-06-01), Papadopoulos et al.
Giridhar, Joint Demodulation of Cochannel Signals Using MLSE and MAPSD Algorithms, 1993 IEEE, pp. IV-160-163.
Giridhar, Joint Estimation Algorithms for Cochannel Signal Demodulation, 9113 IEEE, pp. 1497-1501.
Eyuboglu, Reduced-State Sequence Estimation with Set partitioning and Decision Feedback, IEEE 1988, pp. 13-20.
Anderson, Sequential Coding Algorithms: A Survey and Cost Analysis, 9184 IEEE pp. 169-176.
Simon Haykin, Blind Deconvolution, pp. 1-289.

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