The problem of designing a large high-performance, broadband packet of ATM (asynchronous transfer mode) switch is discussed. Ways to construct arbitrarily large switches out of modest-size packet switches without sacrificing overall delay/throughput performance are presented. A growable switch architecture is presented that is based on three key principles: a generalized knockout principle exploits the statistical behaviour of packet arrivals and thereby reduces the interconnect complexity, output queuing yields the best possible delay/throughput performance, and distributed intelligence in routing packets through the interconnect fabric eliminates internal path conflicts. Features of the architecture include the guarantee of first-in-first-out packet sequence, broadcast and multicast capabilities, and compatibility with variable-length packets, which avoids the need for packet-size standardization. As a broadband ISDN example, a 2048*2048 configuration with building blocks of 42*16 packet switch modules and 128*128 interconnect modules, both of which fall within existing hardware capabilities, is presented.>

The knockout switch is a packet-switch architecture recently proposed for high-performance packet networks. In addition to providing point-to-point connections among user pairs, a packet network must often support multicast and broadcast capabilities. Multicast connections differ from point-to-point connections in that each packet is addressed to a number of destinations. Two specific approaches using the knockout switch to provide a practical and efficient means for multicast services under both light and heavy traffic conditions are proposed. The first involves packet duplication and is more suitable for light traffic loads. The second uses a fast address comparison technique and is capable of handling larger loads. In both cases, the knockout principle is utilized to yield the best delay-throughput performance, guarantee the first-in first-out packet sequence, and provide for a simple, modular implementation.>

The Knockout Switch is a new packet switch architecture recently proposed for high-speed local and metropolitan area networks, multiprocessor interconnects, and local or toll switches for integrated traffic loads. We describe an approach to extend the original Knockout Switch to work with variable-length packets. This new architecture employs an input broadcast bus arrangement to achieve complete interconnection of the inputs and outputs. Consequently, there is no congestion in the switch fabric other than the unavoidable conflict of multiple simultaneous packets destined for the same output. It is with this output contention that the Knockout principle is fully utilized to efficiently concentrate and store contending packets while maintaining the first-in first-out discipline of the packet sequence; and yet the fabric speed required is no more than the input/output line speeds, Under these design goals, no switch can yield better delay/ throughout performance. These are the most important attributes that have been preserved in the current proposal from the original Knockout Switch. For anN \times Nswitch configuration, the variable-length packet Knockout Switch consists ofNinput broadcast buses, and anN:Lconcentrator (L \ll N) and a shared buffer for each output. The design of each subsystem is discussed with emphasis on possible VLSI realization. Using today's technology, we should be able to implement the proposed switch with both input/output lines and internal hardware operating at 50 Mbits/s. The dimension of the switch (N \times N) can grow modularly from say 32 × 32 to 1024 × 1024, rendering a total throughput in the range of tens of gigabits per second. Future upgrading of the line interfaces to much higher speed without modification to the internal switch hardware is also possible with a modest restriction on the minimum length of new packets.

A new, high-performance packet-switching architecture, called the Knockout Switch, is proposed. The Knockout Switch uses a fully interconnected switch fabric topology (i.e., each input has a direct path to every output) so that no switch blocking occurs where packets destined for one output interfere with (i.e., block or delay) packets going to different Outputs. It is only at each output of the switch that one encounters the unavoidable congestion caused by multiple packets simultaneously arriving on different inputs all destined for the same output. Taking advantage of the inevitability of lost packets in a packet-switching network, the Knockout Switch uses a novel concentrator design at each output to reduce the number of separate buffers needed to receive simultaneously arriving packets. Following the concentrator, a shared buffer architecture provides complete sharing of all buffer memory at each output and ensures that all packets are placed on the output line on a first-in first-out basis. The Knockout Switch architecture has low latency, and is self-routing and nonblocking. Moreover, its Simple interconnection topology allows for easy modular growth along with minimal disruption and easy repair for any fault. Possible applications include interconnects for multiprocessing systems, high-speed local and metropolitan area networks, and local or toll switches for integrated traffic loads.

Signal-to-interference ratio statistics for mobile telephony systems with hexagonal coverage areas, multiple interferers, and threecorner base stations are investigated. Corner base stations simultaneously reduce total interference (because of antenna directivity) and provide macrodiversity against shadow fading. Our results indicate that for 3 or 7 channel sets, with 2 tiers of interferers and typical system parameters (propagation exponent of 3.7 and lognormal spread of 8 dB), the improvement is on the order of 11 dB over a baseline arrangement which employs centrally located omnibase stations without macrodiversity. Additional considerations of blocking probabilities and average voice activity indicate possible further improvements.

The mobile radio channel is characterized by three important factors: path losses larger than free space, fading typically taken as Rayleigh, and shadowing generally characterized as lognormal. For cellular systems, in order to determine acceptable reuse distances between base stations and to compare modulation methods, the probability of unacceptable cochannel interference (outage probability) has to be determined in the realistic situation where both fading and shadowing occur. In this paper, the average outage probability is computed for centrally located base stations when multiple log-normal interferers are present. This is done for both the mobile-to-base and base-to-mobile communication links. An unexpected result of this study is that the outage probabilities for the two cases do not differ in a significant way. Cumulative probability curves of the short-term average-signal-toaverage-interference ratio (SIR) are presented for a variety of system parameters: channel set number, propagation law exponent (γ), and dB spread (σ) of the log-normal distribution for the signal and interferers. An important observation is the large sensitivity of the performance curves to the propagation parameters: for a system with seven channel sets with a 10 dB SIR threshold, the average outage probability varies from 10 percent for\gamma = 3.7, \sigma = 6dB, to 70 percent for\gamma = 3, \sigma = 14dB. Alternatively, for a fixed outage objective of 10 percent, the required SIR threshold value ranges from -17 dB to 11 dB, depending on the propagation parameters. These variations make it imperative that accurate measurements of these parameters be obtained for the different service areas. Outage probabilities are also easily related to specific modulation methods and diversity approaches; detailed results are given for several representative cases.

The authors discuss several designs for self-steering array combiners together with a simple frequency-offset tagging method which permits locking of combiner to one of several cochannel but spatially separate signals. The combiners use the output signal as a reference for extraction of phase information from each individual element-signal, thereby utilizing the full transmitted signal for element phase measurement. Designed for receiving PSK signals, the combiner inherently provides, as part of its design, the CW signal required for coherent demodulation of the combined array output. Laboratory measurements made with a four-branch combiner for two-phase PSK signals demonstrate the salient features of the combiner.

Space diversity combining is a well-known method of smoothing amplitude fluctuations of the received signal in Rayleigh fading environments, such as mobile radio. Perhaps less well known is that space diversity combining can also be an excellent method of combating cochannel interference. In this paper, it is shown that high spectrum efficiencies in mobile radio systems can be achieved with a modest number of space diversity branches. With a large number of diversity branches it is shown that frequency reuse is possible resulting in spectrum efficiencies, as defined herein, greater than 100 percent.