Multiplex communications – Diagnostic testing – Determination of communication parameters
Patent
1995-08-28
1997-03-25
Olms, Douglas W.
Multiplex communications
Diagnostic testing
Determination of communication parameters
375232, H04L 2530
Patent
active
056152086
DESCRIPTION:
BRIEF SUMMARY
1. BACKGROUND OF THE INVENTION
The invention relates to the problem of adaptive data detection in a mobile radio receiver. "Adaptive" means that a device is provided in the receiver, which device can understand the time changes of the properties of the mobile radio channel. Such devices normally operate using the LMS (Least Mean Squares) (see for example, citation [1]), or the RLS (Recursive Least Squares) (see for example, citation [2]) algorithm. These algorithms adapt to the properties of the transmission channel continually with time.
EP-A-520 969 specifies an estimation method for data detection, in the case of which received samples in a time slot are initially stored and processed starting with the first received value, to be precise to beyond a fading incursion; further processing is then carried out, starting with the last stored sample, in order to produce estimated values of the transmitted data.
A Kalman filter for adaptation of the channel impulse response in a mobile radio receiver is described in Fifth European Signal Processing Conference, Sep. 18-21 1990, Barcelona, ES; Elsevier, Amsterdam, NL, 1990; pages 225-228, Morgul & Dzung: "New optimum recursive parameter estimation/detection using unreliable erasure declaring detectors". In this case, the Kalman algorithm is applied only to the channel impulse response which is present at a specific time.
The present patent application shows that the algorithms which are continuously adapted with time fail under certain conditions, which are typical for mobile radios. The reason for this is that such adaptation algorithms can be regarded as time-variant first order recursive filters. Higher order algorithms exhibit a behavior which is better in principle.
FIG. 1 shows the data structure which are transmitted in TDMA bursts in a GSM mobile radio system.
FIG. 2 shows a block diagram of the transmission path.
FIG. 3 illustrates the splitting of a TDMA burst into sectors.
FIG. 4 shows a fading incursion in a TDMA burst.
FIG. 5 illustrates a process model relating to the Kalman theory.
2.1 MODEL OF THE TRANSMISSION SYSTEM
In digital TDMA mobile radio systems, the data are transmitted in bursts. In the GSM system, 116 data bits, for example, are combined to form a burst. The burst structure which is chosen for this purpose is illustrated in FIG. 1. In addition to the 116 data bits, which are grouped into two sections of 58 bits each, the burst also includes at each of the ends 3 so-called "tail bits" and in the center a so-called test sequence, comprising 26 bits, so that the burst comprises a total of 148 bits.
The test sequence is used to "survey" the transmission channel. This transmission channel can be regarded as a linear time-variant filter [4] and surveying of the transmission channel thus has the same meaning as an estimate of the channel impulse response.
A measure of the rate of change of the channel is the so-called Doppler frequency ##EQU1##
where f.sub.0 is the carrier frequency of the transmitted signal, v the speed of the mobile subscriber and c the speed of light. The length of a burst is selected such that, despite the possible changes, the channel impulse response during a burst can be regarded as being virtually constant. In the case of GSM, this assumption is valid for speeds v of up to about 250 km/h (the carrier frequency f.sub.0 is around 900 MHz, and the burst duration is around 546 .mu.s).
The method according to the invention is predicated on a burst transmission similar to that in the case of GSM. In particular, the presence of a test sequence in the center of the burst is significant.
Those parts of the transmitter and receiver which are important for the definition of the signals are illustrated in FIG. 2. The modulator maps the data sequence a to be transmitted into the signal s(t). It is assumed that s(t) is a complex low-pass signal having the quadrature components s.sub.I (t) and s.sub.Q (t), that is to say
In this case, j=.sqroot.-1 is the imaginary unit. It is furthermore assumed that W.sub.s is the bandwidth of t
REFERENCES:
D'Aria et al, "Fast Adaptive Equalizers for Narrow-Band TDMA Mobile Radio", IEEE Trans. on Vehicular Tech., vol. 40, No. 2, pp. 392-404 May 91.
A. Morgul et al.: "New Optimum Recursive Parameter Estimation/Detection using Unreliable Erasure Declaring Detectors"; Fifth European Signal Processing Conf., 18-21 Sep. 1990, pp. 225-228.
S.N. Crozier et al.: "Reduced complexity short-block date detection techniques for fading time-dispersive channels." In: IEEE transactions on vehicular technology, vol. 41, No. 3, Aug. 1992, pp. 255-265.
G.W. Davidson et al.: "An investigation of block-adoptive decision feedback equalization for frequency selective fading channels." In: Can. J. Ele. Comp. Eng., vol. 13, No. 3-4, Mar. 1988, pp. 106-111.
ANT Nachrichtentechnik GmbH
Olms Douglas W.
Phillips Matthew C.
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