There have been many theoretical and experimental investigations on polarization diversity reception characteristics at base stations. The diversity gain was evaluated based on the distribution of the instantaneous received power in these investigations. The mainstream mobile communication systems are shifting to standardized IMT-2000 systems and the W-CDMA system is one of them. The effect using base station polarization diversity in W-CDMA must be evaluated by considering not only antenna diversity, but also RAKE reception/path diversity. Furthermore, Transmit Power Control (TPC) is applied to overcome the near-far problem of mobile units that maintain a fixed reception power level in W-CDMA systems. Therefore, traditional diversity gain cannot be used as an evaluation metric. This paper proposes a theoretical analysis method for diversity gain using base station polarization diversity in W-CDMA. The evaluation model used for theoretical analysis is verified based on a comparison with the experimental results and the analytical results of the practical diversity gain are clarified.

In this paper, the impact of timing jitter in direct sequence ultra wideband (DS-UWB) system is investigated over multipath fading channel. Also, a novel hybrid direct sequence multiband UWB (DS-MB-UWB) system is proposed to mitigate the impact of timing jitter. We analyze and compare the system performance for conventional DS-UWB and hybrid DS-MB-UWB with Rake receiver in the presence of timing jitter over additive white Gaussian noise (AWGN) and multipath channel. Theoretical framework is developed to calculate the amount of average energy captured in the multipath profiles and symbol error rate (SER) considering the presence of timing jitter. It is found that DS-MB-UWB system, which employs multiple sub-bands is more jitter-robust than conventional DS-UWB systems. Besides, timing jitter is found to have different impacts on DS-UWB and DS-MB-UWB systems corresponding to different parameters such as number of sub-bands employed, pulse shape, center frequency, bandwidth, number of combined paths in Rake receiver and channel power delay profile (PDP). These different impacts are analyzed and discussed in the paper.

Performance of Rake reception of Ultra Wideband (UWB) signals is evaluated from energy capture perspective. In addition to ordinary all Rake (ARake) and selective Rake (SRake) receivers which are considered in conventional spread spectrum communications, we introduce optimum ARake and SRake receivers which include the estimation of delay of the combining multipaths. Impact of pulse-width is discussed on their performances considering the relationship between pulse-width and fading. Time hopping M-ary pulse position modulation (TH-MPPM) and binary phase shift keying (TH-BPSK) are considered as modulation schemes. Extensive simulation results are presented showing the performances of the Rakes introduced using IEEE 802.15.3a UWB channel models (CM1 to CM3). Performance of MPPM is shown for various values of M and modulation parameters. The impact of pulse-width is illustrated mainly using BPSK. It is shown that the total energy capture (i.e. by ARake) strongly depends on the pulse-width, and the shorter the pulse-width the more is the amount. The energy capture also varies a lot for employing either optimum or ordinary Raking method. Energy capture by SRake additionally strongly depends on the number of combined paths until the number is 20 for optimum SRake and 10 for ordinary SRake; however, afterwards saturating effects are seen. Several aspects regarding the performance versus complexity issue of Rake receivers are also discussed.

This paper proposes an ROF ubiquitous antenna architecture for the wireless CDMA system. The proposed system separates each component of independent signals passing through the multipath in radio and optical links, which are gathered at passive double star link, by using RAKE reception and the macrodiversity effect is obtained. Theoretical analysis shows that the proposed system improves BER performance by 22 dB and reduces the transmission power and its control range by 19 dB.

This paper describes a method of predicting transmission performance to be obtained by applying RAKE reception and parallel transmission in realistic urban multipath environments. Delay profiles measured in metropolitan Tokyo at microwave frequencies were used to obtain the impulse responses of radio channels, and the closed-form equations corresponding to the performance of these anti-multipath techniques were derived, by means of the characteristic function method, under the assumption that the phases of the impulse responses are uniformly distributed. Results show that RAKE reception provides bit error rates 100 times lower than bare transmission does, whereas the improvement obtained by using parallel transmission should be especially valuable in broadband communication systems, such as those operating at data rates above 10 Mb/s.

To enhance the anti-fading technique of direct sequence code division multiple access (DS/CDMA) schemes in land mobile radio communication systems, a two-dimensional RAKE reception (2D-RAKE) scheme in beam space digital beam forming (BS-DBF) antenna configuration is proposed. The proposed scheme is applied to cellular base stations where the received signals in the reverse link are relieved from multipath fading by means of enhanced RAKE combining in spacial and temporal domains. Fundamental performance in the reverse link under multipath fading environments is investigated by computer simulation applying a wideband propagation channel model.

The path diversity improvement inherent in direct sequence spread spectrum (DS/SS) signalling under multi-path propagation environments is investigated for mobile/personal radio communications systems that employ DPSK modulation. The bit error rate (BER) performance of post-demodulation selection diversity reception is theoretically analyzed in the presence of noise-only-paths in the time window for diversity combining. Results of laboratory experiments conducted to evaluate the BER performance are also presented. It is shown that the experimental results agree well with the theoretical BER.