M.P. Lotter

Modeling spatial aspects of cellular CDMA/SDMA systems

The probability density functions (PDFs) describing various physical aspects of hybrid cellular code division multiple-access/space-division multiple-access (CDMA/SDMA) networks are derived. All mobile users are considered to be surrounded by a Gaussian bell shape of scattering elements, and a general rule of thumb for the standard deviation of the scattering elements is proposed. Second, in order to describe the distribution of mobile users in the cell, a general PDF describing mobile user distributions is proposed. Using the mentioned distribution a general PDF for the angle-of-arrival (AOA) of signals at the CDMA base station is derived.

CDMA Techniques for Third Generation Mobile Systems

From the Publisher: CDMA Techniques for Third Generation Mobile Systems presents advanced techniques for analyzing and developing third generation mobile telecommunication systems. Coverage includes analysis of CDMA based systems, multi-user receivers, Turbo coding for mobile radio applications, spatial and temporal processing techniques as well as software radio techniques. Special emphasis has been given to recent advances in coding techniques, smart antenna systems, spatial filtering, and software implementation issues. CDMA Techniques for Third Generation Mobile Systems is an invaluable reference work for engineers and researchers involved in the development of specific CDMA systems.

Cellular channel modeling and the performance of DS-CDMA systems with antenna arrays

In this paper, a new channel modeling approach incorporating nonuniform propagation environments is introduced, and the bit error rate (BER) of a direct sequence code division multiple access cellular system incorporating antenna arrays for spatial filtering is derived analytically. Specifically, this paper introduces a channel model for, and analyzes the performance of, a system in an environment where the multipath signals on each of the diversity branches of a RAKE receiver have varying fading characteristics. This scenario would typically describe urban environments where a large number of multipath echoes are present, each with different fading statistics resulting from the nonhomogeneous propagation paths seen by each multipath echo. It is shown that nonuniform fading parameters for multipath signals can severely influence the system performance, especially at high E/sub b//N/sub 0/ levels. Furthermore, it is shown that the conventional assumption of identical fading statistics for all RAKE receiver branches provide a lower bound on the system performance.

Space division multiple access for cellular CDMA

Space division multiple access (SDMA) will form an important part of the new wideband code division multiple access (W-CDMA) standard that will realise the Universal Mobile Telephone System (UMTS). This paper addresses a few issues of importance when SDMA techniques are used in a cellular CDMA system. Firstly a theoretical analysis of a SDMA/CDMA system is performed. The analysis is focused on a single cell, multipath Rayleigh fading scenario. As system performance measure, the bit error rate (BER) is used as the criterion to investigate the influence of user location and number of antennas. An important parameter in a SDMA system is the antenna array element spacing. In our analysis a uniform linear array (ULA) is considered and a measure is defined to determine the optimal antenna element spacing in a CDMA cellular environment. Normally the mobile users in a cell are assumed to be uniformly distributed in cellular performance calculations. To reflect a more realistic situation, we propose a novel probability density function for the nonuniform distribution of the mobile users in the cell. It is shown that multipath, even with antenna arrays, reduces the system performance substantially.

An overview of space division multiple access techniques in cellular systems

This paper provides an overview of the basic principles of smart antenna techniques as applied to the introduction of space division multiple access (SDMA) techniques in current mobile radio networks, as well as in personal communication services (PCS), personal communications networks (PCN) and the universal mobile telecommunication system (UMTS). It is shown qualitatively how SDMA techniques can increase the capacity of cellular network. Furthermore, a new SDMA principle based on the nonhomogeneous quality of service requirements in mobile multimedia networks is introduced with application to systems proposed for UMTS.

A class of bandlimited complex spreading sequences with analytic properties

This paper describes the construction and correlation properties of a new class of analytic, bandlimited complex (ABC) spreading sequences. The sequences are loosely based on the well known Frank-Zadoff-Chu (FZC) sequences and are constructed by placing some constraints on the phases of the FZC sequences. The new class of spreading sequences are shown to have analytical properties, while retaining reasonable correlation properties. In particular, the analytic properties of the sequences facilitate the use of spreading sequences with double the length in CDMA systems. Furthermore, the sequences have a constant signal envelope making them ideal for applications were a peak-to-mean signal power ratio of one is desirable.

Spatial Filtering and CDMA

A number of smart antenna techniques will form an important part of the new Wideband Code Division Multiple Access (WCDMA) standard that will realize the Universal Mobile Telephone System (UMTS). One such technique is High Sensitivity Reception (HSR) which is implemented in the uplink of cellular systems. This chapter addresses a few issues of importance when HSR techniques are used in a cellular CDMA system. Firstly, a brief overview of smart antenna techniques is presented followed by a theoretical analysis of a HSR/CDMA system. The analysis is focused on both micro and macro multi cell, multipath Rayleigh fading scenario’s with imperfect power control. As a system performance measure, Bit Error Rate (BER) is used to investigate the influence of user location, number of antennas and power control error. An important parameter in the design of a HSR system is the antenna array element spacing. In the analysis a Uniform Linear Array (ULA) is considered and a measure is defined to determine the optimal antenna element spacing in a CDMA cellular environment. Normally, the mobile users in a cell are assumed to be uniformly distributed in cellular performance calculations. To reflect a more realistic situation, a novel probability density function is proposed to model the non-uniform distribution of the mobile users in a cell. It is shown that multipath and imperfect power control, even with antenna arrays, reduces the system performance substantially.

AVTR-a random access method for mobile networks

This paper describes a novel adaptive virtual token ring (AVTR) multiple access protocol. The random access method presented is shown to be a spatial derivative of a token ring network. The operation of the system is described with reference to its application in cellular networks capable of providing a range of heterogenous services such as voice and data. Specifically, it is shown how the system can easily be used to perform dynamic quality of service (QoS) management with little additional hardware resources required.

Spatial considerations in the design and simulation of cellular multiple access systems

Some spatial considerations in the design and simulation of cellular communication systems are discussed. In particular, new probability density functions (PDF) are used to describe the location of users in a cellular system and analytical expressions for the PDF of the angle of arrival (AOA) of signals at the subscriber are derived for systems employing directional antennas or smart antennas. These expressions can be used to derive analytic expressions for the bit error rate performance of space division multiple access (SDMA) communication systems.