Path Diversity Gain Research Articles

Sparse index multiple access for multi-carrier systems with precoding

In this paper, we consider subcarrier-index modulation (SIM) for precoded orthogonal frequency division multiplexing (OFDM) with a few activated subcarriers per user and its generalization to multi-carrier multiple access systems. The resulting multiple access is called sparse index multiple access (SIMA). SIMA can be considered as a combination of multi-carrier code division multiple access (MC-CDMA) and SIM. Thus, SIMA is able to exploit a path diversity gain by (random) spreading over multiple carriers as MC-CDMA. To detect multiple users' signals, a lowcomplexity detection method is proposed by exploiting the notion of compressive sensing (CS). The derived low-complexity detection method is based on the orthogonal matching pursuit (OMP) algorithm, which is one of greedy algorithms used to estimate sparse signals in CS. From simulation results, we can observe that SIMA can perform better thanMC-CDMA when the ratio of the number of users to the number of multi-carrier is low.

크로스 토크를 갖는 통계적 전력선 채널 하에 MIMO-OFDM 광대역 전력선 통신

본 논문에서는 스마트 그리드 응용 등을 타깃으로 한 3상 4선 전력선 채널상의 MIMO-OFDM 광대역 전력선 통신방식 (BPLC broadband power line communication)을 검토하고 성능을 분석한다. 실제전력선 채널 환경을 감안하여 기존의 확정적 페이딩 채널 모델 (Zimmennann 모델, MTL 모델 등) 대신 통계적 전력선 페이딩 채널 모델을 채택한다. 본 논문에서는 3상 4선식 전력선을 이용한 <TEX>$2{\times}2$</TEX> MIMO 및 <TEX>$3{\times}3$</TEX> MIMO 방식을 설계하며, 특별히 MIMO 채널 내 안테나 링크 간 크로스 토크의 유무에 따른 전송 용량 손실과 이에 의거한 시스템 성능 분석을 실시한다. 부반송파 간 주파수간섭을 줄여주기 위해 공간주파수 부호화 전송방식을 채택하며 전력선 채널에 적합한 최대비 합성법 (MRC maximum ratio combining)으로 다중 안테나 및 다중 경로 페이딩 다이버시티 이득을 얻는다. 컴퓨터 시뮬레이션을 통해 임펄스 잡음지수의 변화, 용량 손실 비율의 변화, 서로 다른 수신 신호 합성기법 (최대비 합성, 등가이득 합성, 선택적 함성)에 따른 시스템 성능을 비교분석한다. In this paper, we present a MIMO-OFDM broadband power line communication (BPLC) for Smart Grid and its associated applications and analyze its performance over the 3-phase 4-wire power line channels. For practical BPLC system simulation, we adopt the statistical power line fading channel model instead of the existing deterministic fading channel models (Zimmermann model, MTL model, and so on). In this paper, we implement <TEX>$2{\times}2$</TEX> and <TEX>$3{\times}3$</TEX> MIMO schemes using 3-phase 4-wire power lines. We investigate the capacity loss and BER performance of the proposed MIMO system by considering the effect of cross-talk between antenna paths. We choose space-frequency coding in order to reduce frequency interference between subcarriers and employ maximum ratio combining (MRC) that achieves both multiple antenna path diversity gain and multiple fading path diversity gain. We evaluate the proposed system performance through computer simulation in terms of the impulse noise index and the capacity loss ratio and compare the different signal combining schemes including MRC, equal gain combing (EGC), and selection combining (SC).

Sampling Point Selection Scheme for Fractional Sampling-OFDM Receivers on Fast Time-Varying Multipath Channels

Fractional sampling (FS) and Doppler diversity equalization in OFDM receivers can achieve two types of diversity (path diversity and frequency diversity) simultaneously on time-varying multipath channels. However FS with a higher sampling rate requires the large amount of complexity in demodulation. In this paper, a novel sampling point selection (SPS) scheme with MMSE equalization in FS-OFDM receivers is proposed. On fast time-varying multipath channels, the proposed scheme selects the appropriate samples from the fractionally sampled signals. Through the computer simulation, it is demonstrated that with the proposed scheme, both path diversity gain and Doppler diversity gain can increase as compared to a conventional non-SPS scheme.

A coded convolutional spreading CDMA system with turbo equalization for downlink transmission over a frequency selective fading channel

In this paper, a coded convolutional spreading codedivision multiaccess with cyclic prefix (CS-CDMA/CP) system in conjunction with iterative receivers is proposed for synchronous downlink transmission over frequency selective fading channels and its performance is compared with the uncoded CS-CDMA/CP employing maximum-likelihood sequence estimation (MLSE) receiver as well as with the conventional coded direct sequence CDMA (DS-CDMA) employing (maximal ratio combining-) MRC-RAKE. Contrary to the uncoded CSCDMA/ CP system which suffers from performance degradation at low signal-to-noise power ratios (SNRs), it is demonstrated that the proposed scheme can attain almost the full path diversity gain over all SNRs with single-user complexity. Compared with the coded DS-CDMA system with single-user receivers, the proposed system is free from multiuser interference (MUI) whenever the multipath delay of the channel does not exceed the designed maximum delay. It is also demonstrated, moreover, that the proposed system shows a robust performance even if the channel length exceed the designed maximum delay slightly. Because of the subblock structure of CS-CDMA/CP, the proposed system can utilize time-diversity effects, when the channel subjects fast fading, and this greatly improves the resultant performance. Finally, it is shown that the receiver complexity of the proposed system is compared quite favorably with the iterative multiuser receivers for coded DS-CDMA systems of comparable performance.

Analyzing GPS signals to investigate path diversity effects of non‐geostationary orbit satellite communication systems

AbstractThe concept behind path diversity is that a user who can access several satellites simultaneously will be able to communicate more effectively than a user who could only access one. The success of this method depends on the environment, the satellite constellation, and diversity combining technology. This paper explores the path diversity effects of non‐geostationary orbit (NGO) satellite personal communication services, for different degrees of user mobility, under various scenarios, using the constellation of the global positioning system (GPS). Measurements are taken near downtown Taipei. Three types of mobilities (fixed‐point, pedestrian, and vehicular) are examined, and the switch diversity and maximum ratio combining method are applied to determine the path diversity gain and calculate bit error probability. The error probability performance of applying diversity schemes in coherent binary phase shift keying (BPSK) and non‐coherent differential phase shift keying (DPSK) modulations over Rician fading channels are also analysed and evaluated by using the characteristic function method. The results show that fading can be significantly reduced and diversity greatly increased. A significant diversity gain and improvement in bit error rate (BER) can be expected in all cases by simply applying switch diversity scheme. Besides, for the maximum ratio combining method, the results imply that summing two satellite signals suffices to increase diversity and improve the bit error rate performance. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Field test measurement of DS-CDMA RAKE receiver with TWCL in an urban area

This paper presents field test measurement results from a postdetection RAKE receiver system using a time-window control loop (TWCL). TWCL is a code synchronization scheme, and its performance with delay paths is better than the performance, in terms of acquisition and tracking, without delay paths because of the path-diversity effect. This receiver is suitable for systems that use short spreading codes such as wireless local area networks because it employs a matched filter for despreading. The RAKE method is a simple integral demodulation method used to combine correlation peaks including delay paths in a time window, and two-branch-antenna combining diversity is available. A field test is implemented while walking in an urban area, including the no-line-of-sight situation, taking into consideration microcellular systems. The results show that when the bit error rate is 10/sup -3/ and the spreading-chip rate is 4.096 Mchip/s, path-diversity gain from the theoretical differential quadrature phase-shift keying value is more than 12 dB without antenna diversity. This path-diversity gain value corresponds to a path-diversity reception gain of between two and three. Using two-branch-antenna diversity, the total of path- and antenna-diversity gain is up to 18 dB in the no-line-of-sight situation. From the above results, it is clear that this RAKE receiver is effective even in the no-line-of-sight situation and that TWCL provides good performance under the given field conditions.

Cochannel interference reduction and path-diversity reception technique using CMA adaptive array antenna in digital land mobile communications

This paper describes a cochannel interference (CCI) reduction and path-diversity reception technique using a constant modulus algorithm (CMA) adaptive array antenna in digital land mobile communications. In this technique, the incident signals are individually recovered by using a multistage constant modulus (CM) array that consists of a multistage cascade of signal recovering and canceling processes. The recovered signals are sorted into the desired signal and CCI signal, and then the desired signals are combined in order to obtain the path-diversity gain, Performance is evaluated for a Gaussian filtered minimum shift keying signal and /spl pi//4-shifted quadrature phase-shift keying signal. Each signal processing is carried out using block demodulation (e.g., CMA adaptive signal recovering process and signal canceling process). Computer simulation results show that CCI can be reduced efficiently for a high-bit-rate time-division multiple-access system for quasi-static and fading channel conditions and that the bit error rate (BER) performance is improved by combining the desired signals. The extent of the improvement in BER performance indicates the difference in diversity gain between maximal ratio combining and selective combining. This suggests that a CMA adaptive array antenna is equivalent to selective combining diversity reception.

Path diversity for LEO satellite-PCS in the urban environment

A new method for analyzing the propagation aspects of mobile satellite systems is introduced. It consists of: (1) taking fisheye lens images at potential user locations; (2) extracting path state information (clear, shadowed, or blocked) as a function of look angles from the images; and (3) combining each path state for single or multiple satellites in a specific constellation with frequency-appropriate statistical fade models to predict overall performance measures such as fade dependence with elevation angle or path-diversity gain. The advantage of the method is that it minimizes the need for expensive propagation campaigns. The importance of including specular reflections and diffraction under urban blockage conditions is established. From images obtained in urban Japan, a fade-lapse rate with elevation of 0.2 dB/degree is deduced for fades exceeded about 10% of the time. Path-diversity gain for combining and hand-off diversity is found for up to four-fold diversity at a high-, mid-, and low-latitude location for the Globalstar constellation. With two-fold diversity and neglecting implementation losses, the fade margin required for 80% and 95% coverage at mid-latitude urban locations is reduced from 16 to 6 dB and from 25 to 16 dB, respectively.

A rain attenuation model for satellite link attenuation predictions incorporating the spatial inhomogeneity of rainrate

AbstractA model describing the spatial inhomogeneity of rainrate within a rain cell is derived and incorporated into a specific attenuation model to yield a more exact relationship than has been used heretofore relating rainrate and the attendant attenuation at frequencies above 10 GHz. The resulting unified attenuation model relates terrestrial and slant path attenuation, effective propagation distance and path diversity gain to parameters characterizing the earth‐station or stations (e.g. location, height, latitude, elevation angle and baseline distance from another station), the frequency of operation, and the two possible raintypes admitted into the model (i.e. convective rain and residual or debris rain). The model is particularly suited for the theoretical investigation of path diversity gain since this concept owes its existence to spatial inhomogeneity of rainrate.This inhomogeneous rain attenuation model can be interfaced with an appropriate statistical rainrate prediction model, such as the Crane two‐component model, to yield more precise attenuation predictions.

An empirical relationship for path diversity gain

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.