Multibeam cellular communication systems in which multiple services are of interest are considered. An architecture of channel sharing and medium access which can support multiple services with different CIR requirements is proposed. Dynamic channel assignment (DCA) is used to improve channel reuse and to allocate different CIR quality channels within a channel layout which incorporates several frequency reuse patterns. Channels with higher CIR levels are primarily for services that require higher quality communication links, such as data calls, and channels with lower CIR levels are only for services that require lower quality links, such as voice calls. Services that require lower quality links can also access channels with higher CIR levels if channels of lower quality groups are not available. We develop a tractable analytical model for the system using multidimensional birth-death processes with an appropriate state characterization. Theoretical traffic performance characteristics such as blocking probability, forced termination probability and carried traffic are determined.

Hand-offs in cellular communication systems cause interactions among cells that can be modeled using multi-dimensional birth-death process approaches and the concept of system state. However, exact numerical calculation of traffic performance characteristics is hindered by unmanageably large system state spaces even for systems of modest size. Previous analytical models get around the difficulty by isolating a cell of interest and invoking a Poisson process assumption for hand-off arrivals to the cell. The current paper seeks to explore the interactions in more detail. Two additional approximate analytical models are developed for this purpose. Each of these is more complicated than the simple Poisson process model, but is analytically tractable-at least for small system sizes. One model isolates a cluster of cells (rather than just the cell of interest) from the system and invokes a Poisson process assumption for cells on the cluster periphery. Performance is calculated for the central cell. The second model also isolates a cluster of cells surrounding the cell of interest, but uses an equivalent two-state Markov modulated Poisson process (MMPP) to characterize hand-off arrival processes to the cell of interest from each of the neighboring cells. Poisson hand-off arrivals to cells on the cluster periphery are assumed. This approach has fewer states than the cluster approach. It was found that all are in close agreement with the original "single isolated cell, Poisson hand-off arrival model", which requires the least states.

Channel holding times and user mobility are important topics in the study of wireless cellular communications. We present an approach to modeling user mobility and session time which enables both the calculation of teletraffic performance characteristics and a characterization of holding time which agrees with published reports. The model allows both the dwell time and unencumbered session time to have general distributions. A derivation of the channel holding time distribution is given. We then show how the model's parameters can be chosen to fit empirical data including observations of channel holding time.

In modeling teletraffic performance of mobile cellular networks, previous work has made use of the concept of dwell time-a random variable that describes the amount of time a platform remains in a cell, sector, or microcell. The dwell time was characterized as a negative exponential variate or the sum of negative exponential variates. With a suitable state description, this allows the use of the memoryless property of negative exponential variates with the result that the problem of computing the traffic performance characteristics can be cast in an underlying framework based on multidimensional birth-death processes. Many alternative system configurations and issues can be investigated using this approach. In small cell (microcellular) systems, however, cell sizes tend to be much less regular in shape and size, and differences in paths traversed by mobiles have a large impact on dwell time realizations. Succinctly, some mobile platform classes have mobility characteristics that are highly variable, in that the dwell time standard deviation is greater than the mean. The previous models, in which the dwell time is a negative exponential or sum of exponential variates, may not be adequate in such cases because they can only accommodate dwell time variates for which the standard deviation does not exceed the mean. We extend the analytical framework so that highly variable mobilities can be considered while insights, tools, approaches, and formulations that are facilitated by the framework can be exploited. The approach allows computation of major teletraffic performance characteristics for cellular communications in which mobility issues are important. We consider multiple platform types as well as cutoff priority for handoffs. Additional issues can be considered using this same approach. Computational issues are discussed, and some theoretical performance characteristics are obtained to demonstrate the method and compare with previous work.

We previously suggested a new channel sharing method for cellular communications. The method, called channel borrowing without locking (CBWL), allows real-time borrowing of channels from adjacent cells without the need for channel locking in co-channel cells. CBWL with cut-off priority for calls that arise in the cell is presented. This scheme discourages excessive channel lending and borrowing at high traffic load and promotes a more uniform grade of service throughout the service area. An analysis using macro-states and decomposition is devised to evaluate the performance of the scheme. The results are validated by simulation.

In cellular communication systems overlapping coverage areas of nearby base stations provide some users with access to more than one base. This can be used to improve teletraffic performance. Mobile users who are distant from base stations are helped most by this because they are more likely to be in communication range of other nearby bases. Reuse partitioning, on the other hand, tends to be most helpful to users that are close to base stations, because they can use channels from more partitions. This paper considers the combined use of overlapping coverage and reuse partitioning so that all users gain some advantage. We develop an analytical model for such systems. Theoretical traffic performance characteristics are obtained and compared with those for fixed channel assignment schemes. Priority for hand-off calls is considered. Simulation results validate the analysis.

A personal communication system with multiple hierarchical cellular overlays is considered. The system can include a terrestrial segment and a space segment. The terrestrial trail segment, consisting of microcells and macrocells, provides high channel capacity by covering service areas with microcells. Overlaying macrocells cover spots that are difficult in radio propagation for microcells and provide overflow groups of channels for clusters of microcells. At the highest hierarchical level, communications satellites comprise a space segment. The satellite beams overlay clusters of terrestrial macrocells and provide primary access for satellite-only subscribers. Call attempts from cellular/satellite dual subscribers are first directed to the terrestrial cellular network, with satellites providing necessary overlay. At each level of the hierarchy, hand-off calls are given priority access to the channels. The mathematical structure is that of a multilayer hierarchical overflow system. An analytical model for teletraffic performance (including hand-off) is developed. Theoretical performance measures are calculated for users having different mobility characteristics. These show the carried traffic, traffic distribution, blocking, and forced termination probabilities.>

A hierarchical overlaid scheme suitable for high-capacity microcellular communications systems is considered as a strategy to achieve high system performance and broad coverage. High-teletraffic areas are covered by microcells while overlaying macrocells cover low-teletraffic areas and provide overflow groups of channels for clusters of microcells. New calls and handoff calls enter at both the microcell and macrocell levels. Handoff calls are given priority access to channels at each level. The layout has inherent load-balancing capability, so spatial teletraffic variations are accommodated without the need for elaborate coordination of base stations (wireless gateways). An analytical model for teletraffic performance (including handoff) is developed. Theoretical performance characteristics that show carried traffic as well as blocking, handoff failure, and forced termination probabilities are derived. Effects of nonuniform teletraffic demand and channel allocation strategies on system performance are discussed.>

Signal-to-inference ratio calculations for corner-excited cellular communications systems are presented. Specifically, the ratio of median signal power to the sum of median interference powers is considered. The interference model includes cochannel interference, and immediately adjacent as well as nonimmediately adjacent channel interference. Related system parameters are cluster size, receiver, and transmitter filter characteristics, propagation exponent, tier coverage, and directional antenna front-to-back ratio. Both mobile-to-baseand base-to-mobile communications are considered. The method and model used for calculation are more complete than any previously reported in the technical literature. The calculated results show that the effect of adjacent channel interference compared to cochannel interference cannot be ignored in general. In mobile-to-base communications, the effect of immediately adjacent channel interference introduced by an interfering mobile which is very close to the receiving base antenna is serious.>

The effects of adjacent channel interference, together with cochannel interference, for fixed channel assignment patterns in cellular communications systems are considered. Thorough consideration is given to interference produced by emissions in neighboring channels, including immediately adjacent as well as nonimmediately adjacent channels. An approximate mathematical analysis is presented that permits a more complete calculation of the median mobile-to-base and base-to-mobile signal-to-interference ratios than has been available. Patterns of cell frequency assignment that have regularity properties with respect to the performance measures are determined. Formulas for comparison of signal-to-interference-ratio performance for alternative cell/frequency assignment are derived.>

Some CSMA-CD schemes for multiple priority message classes are suggested. For all the schemes, an approximate analytic technique for calculating the mean packet delay (for each priority) at the stable operating point of the system has been developed. The analytic results are tested against computer simulation. A Poisson packet arrival process and a general packet length distribution are considered. The mean packet retransmission delay is a general function of priority and the number of unsuccessful attempts. There is a variation in delay differences among priorities for the different schemes. This allows one to single out the particular scheme that is optimal for a given system delay requirement. Some of the priority schemes possess the desirable property of having less average delay compared to a corresponding nonpriority system.

A generalization of the slotted ALOHA random access scheme is considered in which a user transmits multiple copies of the same packet. The multiple copies can be either transmitted simultaneously on different frequency channels (frequency diversity) or they may be transmitted on a single high-speed channel but spaced apart by random time intervals (time diversity). In frequency diversity, two schemes employing channel selections with and without replacements have been considered. In time diversity, two schemes employing a fixed number of copies or a random number of copies for each packet have been considered. In frequency diversity, activity factor-throughput tradeoffs and in time diversity, delay-throughput tradeoffs for various diversity orders have been compared. It is found that under light traffic, multiple transmission gives better delay performance. If the probability that a packet fails a certain number or more times is specified not to exceed some time limit (realistic requirement for satellite systems having large round trip propagation delay), then usually multiple transmission gives higher throughput.

Three schemes for course acquisition of spread-spectrum signals are compared: stepped serial search, matched filter, and twolevel. Analytical models and formulas are developed which characterize performance in adverse environments. Comparisons are on the basis of miss probability, mean time to search uncertainty region, and relative complexity.

Tracking requirements for a frequency-hopped spreadspectrum system with a view to application in mobile radio are investigated. Models characterizing Rician fading and multiple access or jamming environments are used to formulate signal detection probabilities. These determine the mean time to loss of lock. Optimized tracking in these environments is then considered.

Equations (10) and (16) of the above-named work (ibid., vol. COM-28, Part 11, pp. 1734-1742, Sept. 1980) are corrected.

A scheme for coarse acquisition of spread spectrum signals is described. It is characterized by a two-level acquisition process employing a passive correlator in tandem with a bank of active correlators. A threshold exceedance of the passive correlator initiates an interval of active correlation if any of the active correlators is idle. The scheme combines the rapid search capability of passive correlation with the decision reliability of (long) active correlation. An analytical model based on queuing and detection theory results is developed, and optimization of the scheme is treated. Performance in the presence of background noise with noise jamming and/or CW jamming is analyzed. Theoretical performance curves and a discussion of results are presented for each type of jamming.

Useful formulas are developed for the iterative calculation of the inverse of blocking probability for Erlang loss and Erlang delay systems, and for the determination of offered traffic and blocking probability for Erlang loss systems when the carried traffic and number of servers are given. These formulas which arise in many problems of queueing and communications traffic can be easily programmed. In tests they gave rapid convergence to high accuracy over a broad range of parameter values much greater than the range of usual display.

The traffic carrying capabilities of demand assigned multiple access (DAMA) systems in which requests for communication circuits are transmitted over shared collision type channels to a master controller are investigated. The circuit request protocol permits both busy and blocked responses in addition to circuit allocations. The theoretically maximum traffic capacity is determined and it is shown that even very simple systems of this type can achieve efficient bandwidth utilization in realistic situations.

The performance of orthogonal and quasi-orthogonal tree codes is considered for incoherent and coherent systems. In addition, several alternative receiver structures using hard quantizing and "greatest-of" detection are treated. Upper bounds on error probability are derived and are used as a basis for system comparison. An application of quasi-orthogonal tree codes to a multiple access environment is presented as an example and discussed.

Correction and discussion of results appearing in a recent paper are presented in this correspondence.

Two approximate methods for analysis of large-scale probems using dynamic channel assignment and a cellular structure are described. Such problems arise in the areas of mobile radio telephony and in multibeam satellite systems. The grade of service of individual zones is considered in detail. The problem is analyzed in terms of the carried erlang load rather than in terms of the system states. These methods are shown to be of a much lower order of difficulty than available methods.

The Chernoff bound is used to derive useful approximations for the generalizedQfunction and its complement.

A Bayesian learning algorithm for statistically optimum adaptive gain control (AGC) is derived in which the receiver gain is adjusted during the learning process so that the average cost of excluding the received signal from the receiver's dynamic range is minimized. Application of the approach to the frequently occurring situation of Rayleigh-distributed signals of unknown strength yields a recursive algorithm that can be easily implemented.

Receiver gains are determined that minimize the average cost of excluding a Rayleigh-distributed signal from a receiver's finite dynamic range when a maximum-likelihood estimate of the unknown Rayleigh parameter is used. Optimum performance is independent of the unknown parameter and converges to "exact knowledge" as sample size increases.