Error rate analysis of differentially encoded and detected 16APSKunder Rician fading

Mobile radio systems require highly bandwidth efficient digital modulation schemes because of the limited resources of the available radio spectrum. A theoretical analysis of bit error rate (BER) is presented for the differential detection of differentially encoded 16-level amplitude/phase shift keying (16DAPSK) under Rician fading in the presence of Rayleigh faded co-channel interference (CCI) and additive white Gaussian noise (AWGN). Differential detection comprises eight-level differential phase detection (DPD) and two-level amplitude ratio detection (ARD). Exact expressions for probability distributions of differential phase noise and amplitude ratio are derived for the BER calculation. The calculated BER performance of 16DAPSK is presented for various values of Rician fading K factor, Doppler spread of diffused component, and Doppler shift of the specular component, and is compared with that of 4-16DPSK. It is shown that 16DAPSK is superior to 16DPSK and requires 1.7 (1.6) dB less E_b/N₀ (SIR) at BER=10^-3 in Rician channels with K=5 dB     

Performance of multi-bit differential SQAM in mobile radio channel

A new multi-bit DSQAM (differential superposed quadrature amplitude modulation) for use in bandwidth and power limited digital mobile radio is proposed. A DSQAM signal is generated by a differentially encoded SQAM processor, and is detected by a multi-bit differential receiver combined with a soft decision Viterbi decoder. The simulated BER result shows that, in an AWGN channel, a 5 bit DSQAM modem achieves a 7.2 dB E_b/N₀ improvement over a conventional 1 bit differential receiver. In Rician fading channels, DSQAM demonstrates a high degree of robustness suffering only a minor loss of signal     

BER performance of CMA adaptive array for high-speed GMSK mobilecommunication-a description of measurements in central Tokyo

This paper describes the performance of an adaptive array as a countermeasure to multipath fading for a 256 kbps Gaussian-filtered minimum shift keying (GMSK) mobile communication system operating in the 1.5 GHz band. An adaptive array having four antenna elements is implemented using the digital beam forming concept. The constant modulus algorithm (CMA) is employed for the adaptation process to ease the implementation. Measurements in central Tokyo of the bit error rate (BER) performance and an array pattern arising in the multipath environment are presented. Analysis of the array pattern confirms that the array succeeds in directing nulls to the delayed signals. BER performance shows an improvement in E_b/N₀, compared with that of a single antenna system, of 17.5 to 22 dB at a BER of 1.0×10^-2 in a frequency-selective fading channel     

Partially coherent DS-SS performance in frequency selectivemultipath fading

The bit-error rate (BER) performance of a direct sequence spread spectrum (DS-SS) signal, operating over a multipath Rayleigh fading channel, is investigated when corrupted by phase noise as well as additive white Gaussian noise (AWGN). The phase noise arises from phase locked loop (PLL) dynamics and results in imperfect receiver phase estimates whereby the phase errors assume Tikhonov densities. The phase estimates are used by a multipath-combining RAKE receiver for demodulation. Approximate upper-bounds on the bit error probability are obtained and evaluated for different combinations of channel parameters and for various values of the average loop signal-to-noise ratio (SNR). Results indicate that for a PLL with loop SNR 10 dB above the system E _b/η₀, the degradation is less than 3 dB, and for a loop SNR of 20 dB above E_b/η₀, the degradation is less than 1 dB     

Binary PRCPM with differential phase detection and maximal ratiocombining diversity in fading channels

We derive a formula for the bit-error probability (BEP) of binary partial-response continuous-phase modulation (PRCPM) with N-bit differential phase detection (DPD) in a Rician fading channel subject to L-branch maximum ratio combining (MRC) diversity. We compute the BEP for minimum-shift keying (MSK), Gaussian MSK (GMSK), and 2 RC (2-b-duration raised cosine) frequency signals as a function of the energy-to-noise ratio per bit E_b/N₀ and other system and channel parameters [N=1 and 2 and L=1, 2, and 3, Rician factor K=-∞, 0, 6, 10, and ∝ dB, Doppler frequency shift f_DT=0, 0.01, and 0.02, Gaussian premodulation filter bandwidth B_gT=∞, 0.5, 0.25, and the presence or absence of a Doppler frequency tracking loop (DFTL) in the receiver]. In all cases, the BEP is significantly reduced by diversity     

Pilot symbol-assisted coherent multistage interference cancellerusing recursive channel estimation for DS-CDMA mobile radio

A pilot symbol-assisted coherent multistage interference canceller using recursive channel estimation is proposed for DS-CDMA mobile radio cellular system. Since the channel variation caused by fading is recursively estimated at each interference cancelling stage, the accuracy of channel estimation is improved successively. Computer simulation results show that the required E_b/N₀ at the average BER of 3×10^-2 is improved by ~3.5 dB compared to the matched filter receiver for 10 users and two paths with equal power, and where f_dT=10^-3 (f_d: fading maximum Doppler frequency, T: data symbol duration)     

Variable rate data transmission with blind rate detection forcoherent DS-CDMA mobile radio

A variable rate data transmission scheme with blind rate detection is described for pilot-symbol-assisted coherent DS-CDMA mobile radio. Cyclic redundancy check (CRC) coding and decoding is used for blind rate detection. Computer simulations of eight-rate variable rate data transmission demonstrate that when 16 bit CRC is used, the loss in required total E_b/N₀ at a frame error rate of 10 ^-2 under two-path Rayleigh fading, is only ~0.1 dB from the known rate case     

Path diversity for FFH/PSK spread-spectrum communication systems

A fast frequency hopping (FFH) method which uses path-diversity combining is proposed. Diversity techniques are realized when a signal is received from diverse independent paths, each of which carries identical information but suffers from independent fading variations. The improvement of communication performance of FFH systems is possible as the delayed paths are used and path-diversity combination is realized. The advantages of this method, operating in Rayleigh fading channels are confirmed by theoretical analyses. The improvement is in order of 2~3 dB at bit error rate (BER) of 10^-3. This method can be also effective against interferences from other users in a code division multiple access (CDMA) environment. The performance of this system in a CDMA environment is evaluated by theoretical analyses and is shown to be superior to non-combining method. At BER of 10^-3 the required E_b/N₀ of the proposed system is 5 dB lower. If E_b/N_o is fixed, a greater number of users can be accommodated using the proposed system     

Coherent orthogonal filter using pilot symbol-assisted channelestimation for DS-CDMA

A coherent orthogonal filter (COF) using pilot symbol-assisted channel estimation is proposed for DS-CDMA cellular mobile radio. In the proposed scheme, a complex fading envelope in the multi-path environment is estimated using pilot symbols, and tap coefficients of orthogonal filter are controlled for maximising the signal to interference ratio (SIR) of a RAKE combined signal. Computer simulation results show that the required E_b/N₀ of the proposed COF is reduced by ~10.0 dB compared to conventional matched filter receiver at an average BER of 3×10² when there are 10 users and processing gain is 31     

M-ary CPFSK-DPD with L-diversity maximum ratio combining in Ricianfast-fading channels

We derive a formula for the bit error probability (BEP) of M-ary continuous phase frequency shift keying with differential phase detection and maximum ratio combining diversity in Rician fast-fading channels. We assume that transmitter and receiver filters distort the signal and limit the noise. We compute the BEP as a function of energy-to-noise ratio per bit (E_b/N₀) and other system and channel parameters: Rician factor K=0, 6 dB, 10, ∞; number of diversity channels L=1, 2, 3; Doppler frequency shift f_D T=0, 0.01, 0.02; Butterworth filters in transmitter and receiver of order N_T=3 and N_R=4; optimal sampling time and filter bandwidth. In all cases the BEP is significantly reduced by diversity     

A new carrier recovery circuit for land mobile satellitecommunication

A DCF (dual carrier filter) reverse-modulation-type carrier recovery circuit is proposed to achieve a low carrier skipping rate and satisfactory phase tracking performance for coherent detection of PSK (phase shift keying) signals in fast Rician fading channels. The proposed scheme employs both narrow and wide bandwidth carrier filters simultaneously for the reverse-modulation-type carrier recovery circuit. It is clarified by computer simulation that the Pe performance of a QPSK (quadriphase shift keying) modem employing the proposed scheme shows an improvement of 1.5 dB in required E_s/N_O at Pe=10⁴ (after Viterbi decoding (R=7/8, K=7), C/M (direct-to-multipath signal power ratio)=10 dB, interleaving size=64×64), compared with conventional coherent detection employing the reverse modulation tank-limiter scheme or the Costas loop scheme     

A Turbo Detection and Sphere-Packing-Modulation-Aided Space-Time Coding Scheme

A recently proposed space-time block-coding (STBC) signal-construction method that combines orthogonal design with sphere packing (SP), referred to here as STBC-SP, has shown useful performance improvements over Alamouti's conventional orthogonal design. In this contribution, we demonstrate that the performance of STBC-SP systems can be further improved by concatenating SP-aided modulation with channel coding and performing demapping as well as channel decoding iteratively. We also investigate the convergence behavior of this concatenated scheme with the aid of extrinsic-information-transfer charts. The proposed turbo-detected STBC-SP scheme exhibits a "turbo-cliff" at E_b/N₀=2.5 dB and provides E_b/N₀ gains of approximately 20.2 and 2.0 dB at a bit error rate of 10 ^-5 over an equivalent-throughput uncoded STBC-SP scheme and a turbo-detected quadrature phase shift keying (QPSK) modulated STBC scheme, respectively, when communicating over a correlated Rayleigh fading channel.A condensed version of this paper was presented at VTC'04 Fall, LA, USA     

Adaptive differential detection using linear prediction for M-aryDPSK

This paper proposes a novel adaptive differential detection scheme (adaptive DD), which can significantly reduce the irreducible bit-error rate (BER) of M-ary DPSK due to Doppler spread by the adaptive linear prediction of the reference signal. The predictor coefficient is adapted to changing channel conditions by using the recursive least-square (RLS) algorithm. A phase sequence estimation based on the M-state Viterbi algorithm (VA) and another based on the decision feedback algorithm (DFA) are presented. A theoretical BER analysis is presented for adaptive DD-DFA. BER performances of 2 and 4DPSK in Rayleigh fading channels are evaluated by computer simulations. When the RLS forgetting factor of β=1 is used, simulation results show that the irreducible BER of 4DPSK can be reduced to 7.2×10^-5 (3.9×10 ^-4) for VA (DFA) while conventional DD offers 3.9×10 ^-3 when f_DT_b (maximum Doppler frequency times bit duration)=0.01 and average E_b/N₀ (signal energy per bit-to-additive white Gaussian noise (AWGN) power spectrum density ratio)=60 dB, where most errors are produced by Doppler spread. Adaptive DD is also effective in AWGN channels-simulations show that for the case of 4DPSK, a performance gain of 1.2 (0.7) dB is achieved over conventional DD for VA (DFA) at BER=10^-3     

DS-CDMA RAKE receiver with time-window control loop (TWCL) inmultipath fading environment

This paper presents a code synchronization scheme-the time-window control loop (TWCL)-for postdetection RAKE receiver systems that offers the path-diversity effect. Laboratory test results from a postdetection RAKE receiver system with TWCL under a frequency-selective fading environment are introduced. RAKE combining methods, a simple integral demodulation method within a time window, and a recursive least squares (RLS) demodulation method within the time window that uses the RLS algorithm to realize maximal ratio combining, are investigated. It is found that TWCL performance with delay paths (double-spike frequency-selective Rayleigh-fading model) surpasses the performance of both acquisition and tracking without delay paths (nonfrequency-selective Rayleigh-fading model) because of the path-diversity effect. The laboratory results show that TWCL provides good acquisition and tracking performance under the fading conditions experienced with maximum Doppler frequencies of 5 or 80 Hz. It is also shown that the signal energy per bit to noise-power spectral-density ratio (E_b/N₀) required to achieve the bit error rate (BER) of 10^-3 under the double-spike frequency-selective Rayleigh-fading model is reduced by 10 dB compared to the nonfrequency-selective Rayleigh-fading model. The difference in path-diversity effect between the two RAKE combining methods is only 1 dB. From a structural viewpoint, the simple integral demodulation method supports miniaturization and high-speed data-transmission     

An Optimum Blind Receiver for Correlated Rician Fading MIMO Channels

A blind receiver scheme for narrowband separately- correlated Rician block fading coded MIMO systems is described. It is shown that this receiver (which can be interpreted as a limiting case of the optimum pilot-aided receiver) attains the maximum achievable throughput at sufficiently high E_b/N₀ ratio. The influence of the E_b/N₀ ratio and of the channel Rice factor on the receiver performance are studied and it is shown that, as either of these parameters increases, the advantage of the blind versus the pilot-aided receiver becomes more sensible. The results obtained support the intuition that, if the line-of-sight component is sufficiently strong, a blind scheme using only the knowledge of the fading statistics parameters matches or outperforms pilot- aided detection.     

Performance of four-dimensional digital communication system infading channels

The authors derive a formula for the bit-error probability (BEP) of a four-dimensional signal and coherent but simple detector in fading channels with Rician or Nakagami probability density function for the received signal envelope. They compute the BEP in both cases and show its dependence on the energy-to-noise ratio per bit, E_b/N_o and channel parameters, K and m, respectively     

Performance evaluation of COFDM for digital audio broadcasting. II.Effects of HPA nonlinearities

For pt. I see ibid. vol.43, no.1, p.64-75, 1997. The effects of the high power amplifier (HPA) nonlinearities on the performance of the Eureka 147 DAB system are studied by computer simulation. The performance is determined for three types of HPA: a travelling wave tube amplifier (TWTA), a solid state power amplifier (SSPA) and a perfectly linearized amplifier (PLA). Two related performance criteria are used: (a) the degradation, resulting from HPA nonlinearities, in the E_b /N₀ ratio required at the receiver to maintain a bit error rate of 10^-4 and (b) the total power degradation. These degradations are measured as a function of the HPA output backoff (OBO). The effect, on the E_b/N₀ degradation, of linearizing only the phase or only the amplitude transfer characteristic of the TWTA and the SSPA is also assessed. Correcting the phase distortion alone in both HPAs is found to reduce the E_b/N₀ degradation by less than 0.5 dB. Linearization of the amplitude characteristic alone, on the other hand, can reduce the E_b/N₀ degradation by several dBs at small OBO values (<2 dB). The optimum output backoff which minimizes the total power degradation is between 2 and 3 dB for both the TWTA and the SSPA in a terrestrial mobile channel and between 1 and 2 dB in an AWGN channel. The optimum output backoff for the PLA is 2 dB in the terrestrial channel and between 1 and 2 dB in the AWGN channel. At the optimal operation point, the power saved by linearizing the amplitude and phase characteristics of the TWTA or the SSPA is about 0.6 dB for the terrestrial mobile channel and 0.4 dB for the AWGN channel     

Experimental evaluation of combined effect of coherent RAKEcombining and SIR-based fast transmit power control for reverse link ofDS-CDMA mobile radio

The combined effect of coherent RAKE combining using the weighted multislot averaging (WMSA) channel estimation filter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K=2 WMSA channel estimation filter reduces the required E_b/I₀ at the average BER of 10^-3 by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E_b/I₀ is minimized when the SIR measurement interval is M=10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results obtained in an area nearby Tokyo showed that the average BER of 10^-3 is achieved at the target E_b/I₀ per antenna of approximately 2.5 dB by using four-finger branch RAKE and two-branch antenna diversity. Although the target E_b/I₀ to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent RAKE combining and fast TPC works well in practical multipath fading channels     

CD3-OFDM: a novel demodulation scheme for fixed and mobilereceivers

This paper describes a novel channel estimation scheme identified as coded decision directed demodulation (CD3) for coherent demodulation of orthogonal frequency division multiplex (OFDM) signals making use of any constellation format [e.g., quaternary phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 64-QAM]. The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalization, therefore yielding a significant improvement in spectrum efficiency (typically between 5-15%). The performance of the system with QPSK modulation is analyzed by computer simulations, on additive white Gaussian noise (AWGN) and frequency selective channels, under static and mobile reception conditions. For convolutional coding rate 1/2, the results indicate that CD3-OFDM allows one to achieve a very fast adaptation to the channel characteristics in a mobile environment (maximum tolerable Doppler shift of about 80 Hz for an OFDM symbol duration of 1 ms, as differential demodulation) and an E_b /N₀ performance similar to coherent demodulation (e.g., E_b/N₀=4.3 dB at bit-error rate (BER)=2·10 ^-4 on the AWGN channel). Therefore, CD3-OFDM can be suitable for digital sound and television broadcasting services over selective radio channels, addressed to fixed and vehicular receivers     

Design, analysis, and performance evaluation for BICM-ID withsquare QAM constellations in Rayleigh fading channels

We consider bit-interleaved coded modulation with iterative decoding (BICM-ID) for bandwidth-efficient transmission over Rayleigh fading channels. We propose the design criteria that utilize a large Hamming distance inherited in a low-rate code and a new labeling technique designed specifically for fading channels. This results in a large coding gain over noniterative coded modulation and performance close to that of “turbo” coded modulation with less complexity. We also show that BICM-ID designed for fading channels usually has a very good performance over the additive white Gaussian noise (AWGN) channel while the converse is difficult to achieve. When combined with signal space diversity, diversity order can be improved to twice the diversity order of conventional BICM-ID; therefore, the code complexity can further be reduced while maintaining the same level of performance. Specifically, with the bandwidth efficiency of 2 bits/s/Hz over Rayleigh fading channels, a bit error rate (BER) of 10^-6 can be achieved with 16-QAM, a four-state rate 1/2 code at E_b/N₀ of about seven dB. We also derive performance bounds for BICM-ID with and without signal space diversity over Rayleigh fading channels, which can be easily extended for other types of fading channels