Modern Probability Theory and Its Applications

We simulate the performance of an equalized Gaussian minimum shift keying (GMSK) signal in an indoor radio environment with fading, noise, imperfect carrier recovery, cochannel interference (CCI), and intersymbol interference (ISI). We show that data rates of 20 Mb/s at bit error rates (BER) /spl les/10/sup -4/ are possible with root mean square (RMS) delay spreads up to 25 ns using a simple limiter-discriminator-integrator (LDI) receiver and a (6, 4) decision feedback equalizer (DFE). In environments with larger RMS delay spreads, coherent detection is required for the same performance. We show that using a decision-directed second-order digital carrier synchronizer with time varying loop filters, frequency offsets up to 200 kHz can be corrected with negligible performance degradation. This paper utilizes a DFE structure which compensates for both modulator and channel ISI, and yet requires no power-intensive multiplication operations in the feedback section. A DFE (8, 8) with two-level switched (selection) diversity is shown to allow 20 Mb/s data transfer at a BER/spl les/10/sup -4/ for RMS delay spreads under 150 ns, with CCI. A light BCH (26, 31) code allows error-free reception of over 90% of packets with RMS delay spreads under 150 ns, and up to 70% of packets with RMS delays of 150 ns.

Adaptive DFE for GMSK in indoor radio channels

The authors consider the error probability at large signal-to-noise ratios of rate-1/2 convolutionally encoded CPFSK (continuous-phase frequency-shift keying) with an optimum noncoherent detector on an additive white Gaussian noise channel. The performance is given in terms of a parameter called the minimum squared normalized equivalent Euclidean distance which plays the same role mathematically as the minimum squared normalized Euclidean distance used for coherent detectors. It is shown that by introducing convolutional coding the error performance is significantly improved. The authors propose a decoding algorithm for these convolutionally encoded CPM schemes which is based on a limited tree search algorithm and uses the maximum-likelihood decision rule for noncoherent detection. Computer simulations show that the degradation in error performance compared to the performance of the optimum coherent Viterbi detector is less than 1 dB with a relatively simple noncoherent detector on an additive white Gaussian noise channel for most of the schemes considered. >

Noncoherent detection of convolutionally encoded continuous phase modulation

The performance of conventional and decision feedback differential detection receivers for Gaussian minimum-shift keying (GMSK) signals transmitted in the presence of cochannel interference (CCI) and additive white Gaussian noise (AWGN) is evaluated. For the interference, the authors adopt a model which includes N statistically independent static as well as faded CCI. Various bit-error-rate (BER) performance evaluation results have indicated that the receiver under investigation performs better as compared to other more conventional receiver structures. Especially significant BER improvements are obtained for the static CCI channel. For example, it is shown that with a carrier-to-interference ratio of 14 dB, the performance of a 2-b decision feedback differential receiver outperforms a conventional 2-b differential detector by more than 14 dB (at a BER 10/sup -3/). For the faded CCI, the improvement is less: mainly they result in error-floor reductions of about half an order of magnitude. By comparing the performance of static and faded CCI, it was also found that for a given C/I, the performance of the former would depend on the number of interferers, whereas this is not the case for the latter. >

Differentially detected GMSK signals in CCI channels for mobile cellular telecommunication systems

The BER performance of a land mobile radio communication system with GMSK modulation is analyzed using one-bit differential detection. In particular, the effect of the IF filter bandwidth on the BFR is analyzed. The optimum bandwidth for the IF filter is found to be a function of signal-to-noise power ratio, signal-to-co-channel-signal power ratio, and signal-to-delayed-signal power ratio. Several graphs are presented to illustrate the effect of the IF bandwidth in the presence of Doppler spread and frequency-selective fading. >

BER analysis of GMSK with differential detection in a land mobile channel

The bit-error-rate (BER) performance of premodulation Gaussian filtered MSK (GMSK) using frequency detection (FD) in conjunction with 1 bit decision feedback equalisation (DFE) is theoretically investigated. The introduction of the premodulation filter causes severe intersymbol interference (ISI) in the waveform of the input to the FM modulator. DFE is used for reducing the ISI effect and therefore improving the BER performance. Applying the analysis to additive white Gaussian noise (AWGN) channels (no fading) shows that a 1-bit DFE attains about 8.5 dB Eb/N0 improvement at BER = 10−3for the premodulation filter bandwidth-time product BbT = 0.25 (typical for mobile radio applications) when the receiver predetection bandpass filter bandwidth-time product BT is optimised. It is shown that the effect of error propagation due to DFE is negligible and the exact BER can be well approximated by the BER that is obtained assuming the decision 1-bit prior is correct. The analysis is then extended to the case of Rayleigh fading channels. Both predetection and postdetection diversity reception are considered. When two-branch predetection maximal-ratio combining (MRC) is used, the 1-bit DFE attains about 6.3 dB Eb/N0 improvement at BER = 10−3for BbT = 0.25.

Performance analysis of GMSK frequency detection with decision feedback equalisation in digital land mobile radio

The combined effect of postdetection diversity reception and concatenated channel coding on the BER floor of pi /4-shift QDPSK due to multipath channel delay spread in Rayleigh fading environments is experimentally investigated. Two-branch postdetection MRC diversity and Reed-Solomon BCH concatenated coding are applied. Experimental results show that for a BER floor of 10/sup -5/ the tolerable RMS delay spread can be increased by approximately 70% over the uncoded, diversity reception case. >

Kizuku Ohno

Papers

Performance analysis of GMSK frequency detection with decision feedback equalisation in digital land mobile radio

Combined effect of diversity reception/channel coding on error floor due to delay spread in DPSK mobile radio