It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

The authors present an overview of new multiple access schemes based on a combination of code division and multicarrier techniques, such as multicarrier code-division multiple access (MC-CDMA), multicarrier direct sequence CDMA (multicarrier DS-CDMA), and multitone CDMA (MT-CDMA).

Overview of multicarrier CDMA

The objective of this survey is to provide the readers and practitioners in the industry with a broader understanding of the high peak-to-average power ratio (PAPR) problem in orthogonal frequency division multiplexing (OFDM) systems and generate a taxonomy of the available solutions to mitigate the problem. Beginning with a description of OFDM systems, the survey describes the most commonly encountered impediment of OFDM systems, the PAPR problem and consequent impact on power amplifiers leading to nonlinear distortion. The survey clearly defines the metrics based on which the performance of PAPR reduction schemes can be evaluated. A taxonomy of PAPR reduction schemes classifies them into signal distortion, multiple signaling and probabilistic, and coding techniques with further classification within each category. We also provide complexity analyses for a few PAPR reduction methods to demonstrate the differences in complexity requirements between different methods. Moreover, the paper provides insights into the transmitted power constraint by showing the possibility of satisfying the constraint without added complexity by the use of companding transforms with suitably chosen companding parameters. The rapid growth in multimedia-based applications has triggered an insatiable thirst for high data rates and hence increased demand on OFDM-based wireless systems that can support high data rates and high mobility. As the data rates and mobility supported by the OFDM system increase, the number of subcarriers also increases, which in turn leads to high PAPR. As future OFDM-based systems may push the number of subcarriers up to meet the higher data rates and mobility demands, there will be also a need to mitigate the high PAPR that arises, which will likely spur new research activities. The authors believe that this survey will serve as a valuable pedagogical resource for understanding the current research contributions in the area of PAPR reduction in OFDM systems, the different techniques that are available for designers and their trade-offs towards developing more efficient and practical solutions, especially for future research in PAPR reduction schemes for high data rate OFDM systems.

Peak-To-Average Power Ratio Reduction in OFDM Systems: A Survey And Taxonomy

A historical perspective of orthogonal frequency-division multiplexing (OFDM) is given with reference to its literature. Its advantages and disadvantages are reviewed, and its performance is characterized over highly dispersive channels. The effects of both time- and frequency-domain synchronization errors are quantified, and a range of solutions proposed in the recent literature are reviewed. One of the main objectives of this review is to highlight the recent thinking behind adaptive bit allocation and turbo coding in the context of OFDM. This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10/sup -4/.

Prolog to adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications

This paper presents the advantages and disadvantages of a multicarrier code-division multiple-access (MC-CDMA) system. The transmitter/receiver structure and, the bandwidth of transmitted signal spectrum are compared with those of a conventional direct-sequence (DS) CDMA system, and an MC-CDMA design method, how to determine the number of subcarriers and the length of guard interval is discussed. The bit error rate (BER) lower bounds for DS-CDMA and MC-CDMA systems are derived and their equivalence is theoretically demonstrated. Finally, the BER performance in downlink and uplink channels with frequency-selective Rayleigh fading is shown by computer simulation.

Design and performance of multicarrier CDMA system in frequency-selective Rayleigh fading channels

A radio communication system between a mobile terminal station of a vehicle and a plurality of roadside fixed base stations is so constructed that communication areas of the base stations do not overlap with each other and satisfy the following two conditions. Condition (i): each communication area is defined so that there cannot be a plurality of terminal stations simultaneously. Condition (ii): it is needless to perform multiple access such as time division in the communication area and capable of affording the whole band and all the communication time allocated to one communication area to one terminal station and broad band communication becomes possible. Thus, each mobile terminal station can utilize all the frequency band allocated for service.

Wireless communication system, fixed base station and mobile terminal station

Bit Error Rate Performances of Orthogonal Multicarrier Modulation Radio Transmission Systems

A new pre-discrete Fourier transformation (DFT) combining diversity receiver is proposed for coded orthogonal frequency-division multiplexing systems and investigated in a frequency-selective fading channel. Although the post-DFT combining space diversity receiver is optimum in terms of maximizing the signal-to-noise ratio (SNR) after combining, it requires an increased number of DFT processors, which increases the computational complexity. Since the proposed pre-DFT combining receiver requires only one DFT processor, while achieving space diversity gain, the proposed scheme can drastically reduce the computational complexity. This paper derives the optimum diversity weights for the proposed receiver analytically, in order to maximize the SNR after combining. Computer simulation results show that the proposed scheme can reduce the computational complexity by tolerating a slight performance degradation.

Pre-DFT combining space diversity assisted COFDM

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency Finally, we propose a two-stage frequency offset compensation method

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

This paper proposes a new mobile image transmission system based on the hierarchical modulation scheme for achieving a high quality and high speed digital image transmission in a band-limited fading channel. The proposed system uses a hierarchical QAM (quadrature amplitude modulation) scheme to give unequal transmission reliability depending on the importance of DCT (discrete cosine transform)-based compressed images. Numerical analysis shows that the proposed system is an effective high-quality and high-speed image transmission technique in a fading channel.

Minoru Okada

Papers

Wireless communication system, fixed base station and mobile terminal station

Bit Error Rate Performances of Orthogonal Multicarrier Modulation Radio Transmission Systems

Pre-DFT combining space diversity assisted COFDM

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

A hierarchical image transmission system in a fading channel