Iterative Versus Adaptive Equalizers in Time-Variant Channels

An adaptive array code acquisition for direct-sequence/ code-division multiple access (DS/CDMA) systems was recently proposed to enhance the performance of the conventional correlator-based method. The scheme consists of an adaptive spatial and an adaptive temporal filter, and can simultaneously perform beamforming and code-delay estimation. Unfortunately, the scheme uses a least-mean-square (LMS) adaptive algorithm, and its convergence is slow. Although the recursive-least-squares (RLS) algorithm can be applied, the computational complexity will greatly increase. In this paper, we solve the dilemma with a low-complexity conjugate gradient (LCG) algorithm, which can be considered as a special case of a modified conjugate gradient (MCG) algorithm. Unlike the original conjugate gradient (CG) algorithm developed for adaptive applications, the proposed method, exploiting the special structure inherent in the input correlation matrix, requires a low computational-complexity. It can be shown that the computational complexity of the proposed method is on the same order of the LMS algorithm. However, the convergence rate is improved significantly. Simulation results show that the performance of adaptive array code acquisition with the proposed CG algorithm is comparable to that with the original CG algorithm.

In this paper, we describe the novel concept of broadcast and multicast (BCMC) transmission over high speed downlink packet access (HSDPA), a shared high-speed packet data channel on the downlink defined in the Universal Mobile Telecommunications System (UMTS) standard. We show that the unique features of HSDPA such as link adaptation, channel-sensitive scheduling, and hybrid automatic repeat request (HARQ) can be used to provide performance gains over conventional multimedia broadcast multicast service (MBMS) transmission on the forward access channel (FACH) channel. We address various aspects of system design and performance in the design of a BCMC system over HSDPA, and present a detailed performance analysis using system level simulations. Some of the main objectives of our BCMC design are to enable broadcast and multicast services on HSDPA networks without requiring significant changes to the HSDPA standard in 3rd Generation Partnership Project (3GPP), and to ensure that the solution is backward-compatible with Release 5 HSDPA mobile devices.

One of the key objectives of Universal Mobile Telecommunications System (UMTS) is the realization of enhanced end-user experience through the provision of rich multimedia services, ensuring in parallel an economical delivery cost for service providers. Multimedia Broadcast/Multicast Services (MBMS) framework of UMTS epitomizes the increasing popularity of such applications by efficiently delivering multimedia traffic to a large number of users and optimizing the radio interface of UMTS networks. For exploiting resource efficiency, MBMS specifications consider the Counting Mechanism which decides whether it is more economic to deliver MBMS multicast traffic over point-to-point (PTP) or point-tomultipoint (PTM) bearers. However, the necessity to further improve MBMS resource efficiency and integrate new technologies such as High Speed Downlink Packet Access (HSDPA) stresses the need for an advanced Counting Mechanism. To this direction, in this paper we propose a novel Power Counting Mechanism which performs optimal power resource utilization and incorporates the HSDPA broadband extension of UMTS for enhanced performance.

WiMAX physical layer implemented Orthogonal Frequency Division Multiple Access (OFDMA) as one of the medium to conduct data transmission. OFDMA suffers from Intersymbol Interference (ISI) which can distort efficiency of the signal transmitted. ISI emerges in the system because of multipath. Basic Cascaded Least Square (CLS) with Decision Feedback Equalizer (DFE) had been proposed in previous research to minimize ISI in wireless communication system. This research will improve CLS performance in terms of convergence. CLS is a cascaded of two adaptive algorithms which are Least Mean Square (LMS) and Recursive Least Square (RLS). Although basic LMS has low complexity than RLS and has been used widely in wireless environment, LMS is suffering in terms of convergence. Updated Normalized Least Mean Square (NLMS) with training rate applied in this research to overcome disadvantage in LMS algorithm. This research justified that training rate is an alternative method to improve CLS-DFE in wireless communication system.

This chapter contains sections titled: Introduction High Speed Downlink Packet Access High Speed Uplink Packet Access Implementation Issues

In order to improve support for higher speed data, 3GPP has developed an evolution of UNTS based on WCDMA known as HSDPA(high speed downlink packet access). The target of HSDPA is to provide service for not only voice user but also higher speed data users. For HSDPA, there are two important parameters, which are the rate ratio and the power ratio between higher speed data signal and voice data signal. In this article, we deduced two useful conclusions, which are based on the research of the relationship between the rate ratio and the power ratio. One of the two conclusions is that the transmission power is in positive proportional to data rate when the user numbers of higher speed data is high, which would result in dramatic interference of multi-user. The other is that the same capacity can be achieved by only using half transmission power when there is one higher speed data user over one transmission time interval. Based on the two conclusions, the feasibility of HSDPA is studied. We found that it is impossible for HSDPA to provide simultaneously service for multiple high-speed data users and voice users. A feasible CDMA/TDMA reform scheme is proposed, which can achieve the design goal of WCDMA HSDPA. The reform scheme employs the method of time domain multiplexing(TDM) to realize the transmission of high speed data over a special CDMA channel. The reform scheme can increase dramatically downlink capacity, improve spectral efficiency, and also reduce system cost by employing simple interference eliminator.

Smart antenna systems are of great importance in wireless communication and radar applications. They effectively enhance the system capacity and reduce the co-channel interference. Smart antenna is an array antenna that uses adaptive beamforming algorithms to steer the main beam toward the desired signal direction and reject the interfering signals of the same frequency from other directions without moving the antenna. This is achieved by continuously updating the weights of each radiating element (antenna). An algorithm with low complexity, low computation costs, high speed convergence rates and better performance is usually preferred. This paper introduces a new performance investigation and comparison between five different beamforming algorithms: Least Mean Square (LMS), Normalized Least Mean Square (NLMS), Sample Matrix Inversion (SMI), Recursive Least Square (RLS) and Hybrid Least Mean Square / Sample Matrix Inversion (LMS/SMI). In this investigation, the number of array elements and the displacement among them are changed in each algorithm. Simulation experiments are carried out, and the results are compared to verify the effectiveness of this investigation. The performance of each algorithm is optimized and demonstrated using MATLAB software package.

High speed downlink packet access (HSDPA) is specified in the 3GPP to cope with the increasing demand of high-speed Internet-based multimedia services. HSDPA is based on techniques such as base station scheduling, adaptive modulation and coding, hybrid automatic repeat request, and advanced receiver design. This work presents system-level simulation results on the HSDPA performance to reveal the effects of user equipment (UE) capabilities such as the maximum number of multicodes and receive diversity. The results show that a 15- and 10-multi-code UE and the receive diversity significantly improve the cell capacity. Experiments using the HSDPA test-beds are conducted to investigate the true HSDPA performance. Furthermore, TCP/IP-level simulation results show the application-level throughput, i.e. end-user throughput, in the HSDPA system. The results indicate that reduction of the round trip time, a higher uplink data rate, and low uplink block error rate are required to achieve the high TCP-level throughput.

This paper analyzes the theoretical limits of the Least Mean Square (LMS) and Recursive Least Square (RLS) adaptive algorithms performance for the adaptive CDMA receivers in slowly time varying communication channels in the presence of multi-path. We show that since the RLS involves memory and does not explicitly recognize time varying nature of the channel (time varying "true" weights), it has worse tracking performance then the LMS adaptive algorithm. Thus, the implementation of the RLS algorithm for adaptive CDMA receivers operating in time varying channels is very limited. The LMS algorithm provides better tracking, but still speed of channel change must be slow. In addition, we present simulation results which confirm the theoretical analysis.

The provision of data services in 3G systems requires spectral efficiency solutions to increase the capacity of the radio access network as well as support for high data rates. In this context, the 3GPP introduces a new feature in the release 5 specifications denominated high speed downlink packet access (HSDPA). The HSDPA concept appears as an umbrella of features to improve both user and system performance. The concept includes a reduction of the transmission time interval (TTI) to 2 ms, an adaptive modulation and coding (AMC) scheme, and a fast physical layer hybrid ARQ mechanism. In this paper the objective is to analyze the HSDPA performance for streaming, interactive, and background services. Relevant characteristics such as the QoS demands of the different traffic classes, the throughput and delay characteristics has been analyzed and compared with shared channel. We also propose a new packet-scheduling scheme for HSDPA transmission, which improves the overall performance and fairness among the packet users.

In this paper, a comparison study of various UMTS data transmission techniques is performed. An analysis of the system in the presence of geographically non-uniform multi-service traffic profiles is done for three transmission techniques: Frequency Division Duplex (FDD), Time Division Duplex (TDD), and High Speed Downlink Packet Access (HSDPA). Several combinations were selected: FDD, TDD, FDD combined with HSDPA, FDD combined with TDD, and FDD combined with TDD and HSDPA. The TDD mode is the technique with better results, but the introduction of HSDPA is clearly beneficial for data services, as expected. The distribution of the services by the three techniques is the best scenario, namely for some traffic profiles. For example, for a threshold of 128 kbps (for HSDPA services) and 50 % of the power reserved to HSDPA, it is possible to get 1.4 GB of carried traffic.

Speech enhancement is a vital area of research, the performance of speech based human machine applications such as automatic speech recognition system, in car communication depends on the quality of speech communicated. Different methodologies have been used by various researchers to improve the quality of speech signal. In this paper an attempt is made to analyze the performance of Least Mean Square (LMS) and Recursive Least Squared (RLS) adaptive filter algorithm for speech enhancement application. The performance indices used for the evaluations is Mean Square Error (MSE), Signal to Noise Ration (SNR) and execution time. The detail analysis is done and experimentally the results are validated and certain modifications are suggested in the algorithm. The experimentation revels that LMS have fast convergence than RLS. The computational complexity of RLS is very high as compared to LMS.

In Wideband Code Division Multiple Access (WCDMA) networks the Signaling Radio Bearer (SRB) is transmitted downlink to inform the user i.a. when it needs to make a handover. When transmitting e.g. Voice over IP (VoIP) on High Speed Downlink Packet Access (HSDPA) SRB is mapped on HSDPA user data channel, high-speed downlink shared channel (HS-DSCH) in order to maximize voice capacity. The lack of support for soft handover (SHO) of HS-DSCH may compromise the reception of SRB and thus also a possible incoming serving HSDPA cell change command especially at the cell borders. This can lead to serious VoIP service degradation due to prolonged camping on a poor cell and in the worst case even to call dropping, if the cell change command is not received before VoIP call drop criterion is met. This paper considers the performance of SRB transmission on source cell HS-DSCH during a handover process. Also a strategy of transmitting the serving cell change command from the target cell is analyzed. The study is done by the means of fully dynamic system simulations and they consider both macro-cell and manhattan scenarios. The results show that a relatively low SRB/handover error rate is experienced in a macro cell scenario but in a more challenging manhattan scenario the error rate is higher. Transmitting the serving cell change command from the target cell HS-SCCH results in similar handover failure rates in manhattan scenario than using SRB on HS-DSCH in macro-cell scenario when static power allocation for HS-SCCH is in use.

We propose an method of implementing simultaneously despreading operation for high speed downlink packet access (HSDPA) wideband code division multiple access (W-CDMA) signals using fast Fourier transform (FFT). HSDPSA is a part of the W-CDMA standard and it provides an access method for high speed data communications. The basic idea of the HSDPA is similar to that of the orthogonal frequency division multiplex (OFDM), namely, instead of using multiple frequency to transmit symbols, HSPDA uses multiple spreading codes to transmit symbols. Although the idea is same, they uses different transformation for multiplexing: OFDM uses the fast Fourier transformation (FFT) and, on the other hand, HSDPA (WCDMA) uses Walsh-Hadamard transformation (WHT). Therefore, it becomes hard to implement these two technologies into a single configuration. The proposed method implement the despreading process as a combination of an FFT and a post-processing. By computer simulation, it is shown that the proposed method provides same BER performance with that of the direct despreading calculation. Moreover, we show that, by generalizing the configuration of the proposed method, WCDMA can be expressed as a special case of the multicoded multicarrier (MC-MC) CDMA. MC-MC CDMA is a newly proposed multiplexing method and is a mixture of the OFDM and CDMA technologies. We show that all of OFDM, MC-MC CDMA and WCDMA can be implemented by a combination of an FFT and a multiplication of orthogonal matrix. Hence, using the proposed method, we can implement those three technologies into a single configuration.

High speed downlink packet access (HSDPA) is a packet-based data service in UMTS networks that supports data rates of several Mbit/s, making it suitable for data applications ranging from file transfer to multimedia streaming. In spite of the fairly high data rates that HSDPA offers, the shared downlink radio channel used in HSDPA is a challenging environment for delay- and loss-sensitive applications. It is relatively easy to partition resources over wired links with known link capacity. Nevertheless, such partitioning is complex for wireless links with variable capacity; due to the dynamic nature of the link, it is difficult to effectively allocate the resources (i.e., time slots) between users who may be paying different prices for different services. In this paper we study the general problem of resource partitioning for shared wireless links like HSDPA. We consider different QoS classes or user groups, and the use of MAC-layer scheduling for resource partitioning between groups and between individual users. We propose a variant of an existing HSDPA scheduler called required activity detection (RAD) scheduler. The proposal is studied using a detailed UMTS/HSDPA simulator.