Reduced cost alternatives to premise wiring using ATM and microcellular technologies

The cost of premises wiring keeps increasing due to personnel moves, new equipment, capacity upgrades etc. It would be desirable to have a wireless interface from the workstations to the fixed network, so as to minimize the wiring changes needed. New technologies such as microcellular personal communication systems are promising to bring down the cost of wireless communication. Another promising technology is Code Division Multiple Access (CDMA), which could dramatically increase the bandwidth available for wireless connections. In addition, Asynchronous Transfer Mode (ATM) technology is emerging as a technique for integrated management of voice, data, and video traffic on a single network. The focus of this investigation will be to assess the future utility of these new technologies for reducing the premise wiring cost at KSC. One of the issues to be studied is the cost comparison of 'old' versus 'new,' especially as time and technology progress. An additional issue for closer study is a feasible time-line for progress in technological capability

Adaptive space-time processing for digital mobile radio communication systems

The performance of digital mobile radio communication systems is primarily limited by cochannel interference and multipath fading. Antenna arrays, with optimum combining (OC), have been shown to combat multipath fading of the desired signal and are capable of reducing the power of interfering signals at the receiver through spatial filtering. With OC, the signals received by several antenna elements are weighted and combined to maximize the output signal-to-interference-plus-noise ratio (SLNR). We derive new closed-form expressions for (1) the probability density function (PDF) of the SINR at the output of the optimum combiner, (2) the average probability of bit error rate (BER) and its upper bound, and (3) the outage probability in a Rayleigh fading environment with multiple cochannel interferers. The study covers both the case when the number of antenna elements exceeds the number of interferers and vice versa. We consider independent fading at each antenna element, as well as the effect of fading correlation. The analysis is also extended to processing using maximal ratio combining (MRC). The performance of the optimum combiner is compared to that of the maximal ratio combiner and results show that OC performs significantly better than MRC. We investigate the performance of OC in a microcellular environment where the desired signal and the cochannel interference can have different statistical characteristics. The desired signal is assumed to have Rician statistics implying that a dominant multipath reflection or a line-of-sight (LOS) propagation exists within-cell transmission. Interfering signals from cochannel cells are assumed to be subject to Rayleigh fading due to the absence of LOS propagation. This is the so called Rician/Rayleigh model. We also study OC for a special case of the Rician/Rayleigh model, the Nonfading/Rayleigh model. We derive expressions for the PDF of the SJNR, the BER and the outage probability for both Rician/Rayleigh and Nonfading/Rayleigh models. Similar expressions are derived with MRC. Another area in which space-time processing may provide significant benefits is when wideband signals (such as code division multiple access (CDMA) signals) are overlaid on existing narrowband user signals. The conventional approach of rejecting narrowband interference in direct-sequence (DS) CDMA systems has been to sample the received signal at the chip interval, and to exploit the high correlation between the interference samples prior to spread spectrum demodulation. A different approach is space-time processing. We study two space-time receiver architectures, referred to as cascade and joint, respectively, and evaluate the performance of a DS-CDMA signal overlaying a narrowband signal for personal communication systems (PCS). We define aild evaluate the asymptotic efficiency of each configuration. We develop new closed-form expressions for the PDF of the SINR at the array output, the BER and its upper bound, for both cascade and joint configurations. We also analyze the performance of this system in the presence of multiple access interference (MAJ)

Performance improvements in wireless CDMA communications utilizing adaptive antenna arrays

This dissertation studies applications of adaptive antenna arrays and space-time adaptive processing (STAP) in wireless code-division multiple-access (CDMA) communications. The work addresses three aspects of the CDMA communications problems: (I) near-far resistance, (2) reverse link, (3) forward link. In each case, adaptive arrays are applied and their performance is investigated. The near-far effect is a well known problem which affects the reverse link of CDMA communication systems. The near-far resistance of STAP is analyzed for two processing methods: maximal ratio combining and optimum combining. It. is shown that while maximal ratio combining is not near-far resistant, optimum combining is near-far resistant when the number of cochannel interferences is less than the system dimensionality. The near-far effect can be mitigated by accurate power control at the mobile station. With practical limitations, the received signal power at a base station from a power-controlled user is a random variable clue to power control error. The statistical model of signal-to-interference ratio at the antenna array output of a base station is presented, and the outage probability of the CDMA reverse link is analyzed while considering Rayleigh fading, voice activity and power control error. New analytical expressions are obtained and demonstrated by computer simulations. For the application of an adaptive antenna. array at the forward link, a receiver architecture is suggested for the mobile station that utilizes a small two-antenna array For interference suppression. Such a receiver works well only when the channel vector of the desired signal is known. The identifying spreading codes (as in IS-95A for example) are used to provide an adaptive channel vector estimate, and control the beam steering weight, hence improve the receiver performance. Numerical results are presented to illustrate the operation of the proposed receiver model and the improvement in performance and capacity

The Impact of Space Division Multiplexing on Resource Allocation: A Unified Approach

Recent advances in the area of wireless communications have revealed the emerging need for efficient wireless access in personal, local and wide area networks. Space division multiple access (SDMA) with smart antennas at the base station is recognized as a promising means of increasing system capacity and supporting rate-demanding services. However, the existence of SDMA at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on channel allocation at the media access control (MAC) layer. This impact obtains different forms in TDMA, CDMA and OFDMA access schemes, due to the different cochannel and inter-channel interference instances, as well as the different effect of corresponding channels (time slots, codes or subcarrier frequencies) on user channel characteristics. We follow a unified approach for these multiple access schemes and propose heuristic algorithms to allocate channels to users and adjust down-link beamforming vectors and transmission powers, with the objective to increase achievable system rate and provide QoS to users in the form of minimum rate guarantees. We consider the class of greedy algorithms, based on criteria such as minimum induced or received interference and minimum signal-to-interference ratio (SIR), as well as the class of SIR balancing algorithms. Our results indicate that this cross-layer approach yields significant performance benefits and that SIR balancing algorithms achieves the best performance

Performance evaluation for communication systems with receive diversity and interference

Optimum combining (OC) is a well-known coherent detection technique used to combat fading and suppress cochannel interference. In this dissertation, expressions are developed to evaluate the error probability of OC for systems with multiple interferers and multiple receiving branches. Three approaches are taken to derive the expressions. The first one starts from the decision metrics of OC. It facilitates obtaining closed-form expressions for binary phase-shift keying modulation. The second approach utilizes the moment generating function of the output signal to interference plus noise ratio (SINR) and results in expressions for symbol and bit error probability for multiple phaseshift keying modulation. The third method uses the probability density function of the output SINR and arrives at expressions of symbol error probability for systems where the interferers may have unequal power levels. Throughout the derivation, it is assumed that the channels are independent Rayleigh fading channels. With these expressions, evaluating the error probability of OC is fast, easy and accurate. Two noncoherent detection schemes based on the multiple symbol differential detection (MSDD) technique are also developed for systems with multiple interferers and multiple receiving branches. The first MSDD scheme is developed for systems where the channel gain of the desired signal is unknown to the receiver, but the covariance matrix of the interference plus noise is known. The maximum-likelihood decision statistic is derived for the detector. The performance of MSDD is demonstrated by analysis and simulation. A sub-optimum decision feedback algorithm is presented to reduce the computation complexity of the MSDD decision statistic. This suboptimum algorithm achieves performance that is very close to that of the optimum algorithm. It can be shown that with an increasing observation interval, the performance of this kind of MSDD approaches that of OC with differential encoding. The second MSDD scheme is developed for the case in which the only required channel information is the channel gain of the interference. It is shown that when the interference power level is high, this MSDD technique can achieve good performance

Study of advanced communications satellite systems based on SS-FDMA

A satellite communication system based on the use of a multiple, contiguous beam satellite antenna and frequency division multiple access (FDMA) is studied. Emphasis is on the evaluation of the feasibility of SS (satellite switching) FDMA technology, particularly the multiple, contiguous beam antenna, the onboard switch and channelization, and on methods to overcome the effects of severe Ka band fading caused by precipitation. This technology is evaluated and plans for technology development and evaluation are given. The application of SS-FDMA to domestic satellite communications is also evaluated. Due to the potentially low cost Earth stations, SS-FDMA is particularly attractive for thin route applications up to several hundred kilobits per second, and offers the potential for competing with terrestrial facilities at low data rates and over short routes. The onboard switch also provides added route flexibility for heavy route systems. The key beneficial SS-FDMA strategy is to simplify and thus reduce the cost of the direct access Earth station at the expense of increased satellite complexity

Network capacity and quality of service management in F/TDMA cellular systems

As a consequence of rapidly increasing mobile communications, efficient utilization of the scarce radio resources becomes one of the most important issues in the system evolution. Increase of the system capacity has been investigated in two ways. The first way is to replace the fixed channel allocation (FCA), with the more efficient dynamic channel allocation (DCA). The second way is to utilize those traffic channels not being used by voice services to provide a packet data service, like general packet radio service (GPRS) and cellular digital packet data (CDPD). In this thesis, the author have proposed two DCA schemes and developed an analysis method to investigate the GPRS impact on the GSM voice services. In addition, the GPRS downlink performance is investigated and some guidelines or principles for GPRS network planning have been presented. In the proposed DCA algorithms, the effect of the channel allocation on existing calls is considered by the evaluation of the call outage rate or a cost function. In the first proposed algorithm, in order to evaluate the call outage caused by those candidate channels, a method of estimating the average signal to interference ratio (SIR) variation of on-going calls due to the assignment of a coming call has been developed. This algorithm improves the capacity or QoS performance compared with the first available and maximum SIR schemes. In the second proposed algorithm, a cost function has been introduced to estimate the cost of the assignment of a candidate channel. The performance evaluation shows that by using the cost-function for channel pre-selection the problem of high intracell handover rate for the first available based scheme can be decreased to an adequate level and the time of the call set-up can be shortened. An analysis method to calculate the outage probability of the GSM-GPRS network for both the non-frequency hopping and frequency hopping systems has been presented to investigate the GPRS impact on GSM voice services. It is found that: GPRS affects more on the QoS of voice services of the network with small reuse factor; GPRS will reduce the cell service area, but the reduction percentage of the cell service area for the system with small reuse factor is higher than that for the system with large reuse factor; those channels unused by voice services might not all be used for carrying GPRS traffic; the number of unused voice channels which can be allocated to GPRS depends on the difference between the outage level of the existing GSM network and the maximum acceptable level. From final part of this work, it is found that: GPRS capacity performance in downlink is quite different from that in uplink because of the difference in the transmission protocols; multiple-slot allocation does not show a gain of the mean throughput neither a decrease on the mean delay compared to single slot allocation. This result is different from the result of the uplink performance. In multi-rate services, the multi-slot services significantly increase the delay of the single-slot service, consequently, a control of the multi-slot services is needed.reviewe