Capture probability in a mobile packet radio system

The probability of q_i of successful packet reception when i users transmit simultaneously in a mobile packet radio system is shown to decrease monotonically with i for a number of commonly used capture and spatial distribution models, with no fading. Examples of both noiseless and noisy systems in which q_i is not monotonically decreasing with i are also given     

Computer simulation of a mobile packet radio system

A software simulator for a mobile packet radio system is described. Bitwise coherent addition of interfering DPSK-packets can be expected, resulting in a smaller throughput than achieved with incoherent addition, but higher than in a nonfading channel     

Transmission algorithms for a multi-channel packet radio system with priority users

In multi-channel systems such as multi-station packet radio networks or cellular radio, various user categories arise. In this paper, we propose that one portion of the users, named low-priority, each be assigned a specific channel for their transmissions, whereas another portion, named high-priority, may transmit through any of the channels via some channel selection policy. The main objective is to reduce delays of the high-priority users without imposing heavy penalties on the delays of the low-priority group. For the described system, we adopt a previously studied limited sensing random access algorithm and introduce two dynamic channel selection policies. We study the stability region and the delays induced by the system. The selection policies present the high-priority users with a significant delay advantage and induce fair utilization of the transmission channels, without requiring any knowledge about the system state by the users. One of the selection policies induces high system throughput at the expense of implementation complexity and increased delays for the low-priority users. The second policy is easier to implement but, although it does not penalize the delays of the low-priority users, it reduces the system thoughput.     

Diversity reception in a multihop packet radio network

The performance improvement which results from the use of multiple antennas at each node in a multihop packet radio network is examined. Four transmission strategies based on three previously proposed routing schemes and one new routing scheme, MTP, are studied. It is found that the use of two antennas can improve the performance of all four transmission strategies by about 25% in a Rayleigh fading environment. The transmission strategy based on the MTP routing scheme is shown to be generally superior to those based on the other three routing schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Diversity reception in a multihop packet radio network

The performance improvement which results from the use of multiple antennas at each node in a multihop packet radio network is examined. Four transmission strategies based on three previously proposed routing schemes and one new routing scheme, MTP, are studied. It is found that the use of two antennas can improve the performance of all four transmission strategies by about 25% in a Rayleigh fading environment. The transmission strategy based on the MTP routing scheme is shown to be generally superior to those based on the other three routing schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

The low-cost packet radio

Research on packet switched radio networks requires reconfigurable testbeds with large numbers of readily deployable radios. This motivated the development of a small, low-cost packet radio (LPR) with the flexibility to support extensive network experiments, and to be amenable to tailoring to specific end-use applications. The LPR incorporates a digitally controlled direct sequence minimum shift keyed spread-spectrum radio and a microprocessor-based packet switch. Code changeable surface acoustic wave (SAW) matched filtering provides processing gain at burst symbol rates of 100k and 400k symbols per second in the presence of interference. Coherent recursive integration enhances synchronization performance, provides synchronous detection of the data, and serves the adaptive multipath accumulator. Forward error correction utilizing convolutional encoding and sequential decoding is incorporated at four different code rates for both burst symbol rates. The microprocessor runs the networking software. Requirements, design, and performance data for the LPR engineering model are presented.     

Wide-band packet radio technology

Advances in signal processing and architectural design for high-performance packet radio are described. The scope of the work roughly encompasses the data-link and physical levels of standardized layered-network architectures. A hardware-function layering approach is used, including the purposeful design of an interface to provide a structured control environment for a demonstration packet radio. The advanced signal processing provides a robust, flexible data link to service demanding network environments, and uses 100-MHz-bandwidth surface-acoustic-wave (SAW) convolvers as large time-bandwidth product matched filters for communication with nonrepeating pseudonoise waveforms. The convolvers are combined with a binary-quantized postprocessor to implement a hybrid correlator which provides high processing gain for detection, demodulation, and ranging measurements. Data rates can be selected, in response to varying channel conditions, over a range from 1.45 Mbits/s down to 44 bits/s with an almost ideal tradeoff in processing gain for interference rejection and privacy ranging from 18 dB up to 61 dB. Future enhancements are proposed that will advance both the signal processing and the architecture.     

基于MIMO系统的天线选择

多天线MIMO（Multiple Input Multiple Output）系统利用多个收、发天线有效地改善无线通信系统性能，提高系统容量，增强系统可靠性。然而，由于使用多天线同时收发，这要求发射机和接收机使用与天线一样多的射频链路，增加了系统成本和复杂度。使用天线选择技术可以降低系统成本和复杂度，同时保留MIMO系统的优越性能。文中首先介绍了MIMO系统的实现方式，然后讨论天线选择的方法及性能，最后提出天线选择技术还存在的问题，并得出相关的结论。     

A slotted ALOHA packet radio system with multiple antennas andreceivers

The problem of data transmission in a mobile packet radio system with one central base station and a number of mobile terminals is addressed. A method using multiple directional antennas and receivers at the base station to improve the efficiency of transmission on the inbound channel (from the terminals to the base station) is proposed. A number of channel models are considered, including flat terrestrial propagation loss, Rayleigh fading, and noise. A finite population Markov model is used to obtain the throughput of a multiantenna and multireceiver slotted ALOHA system. Numerical results indicate that substantial gains are possible with the use of several antennas and receivers. The dynamic behavior of the system is also improved     

Issues in packet radio network design

There are many design choices that must be made in the development of a packet radio network. There is usually no single correct choice, and the decisions are dependent on the environment that the network must work in, the requirements for performance and other functionalities, and the cost and other limitations, in addition, as new hardware and software technologies become available, the parameters governing the decisions change and often result in different selections. This paper outlines a number of design issues and choices available. The intent is to provide an overview of the design decisions that must be made so as to provide a context for the decisions made in a number of existing and developing packet radio networks. It is hoped that this will allow future designs to take advantage of both the wealth of experience available as well as new technologies. Three areas of design decisions are identified. The first area deals with the physical aspects of the network and concentrates on the radio connectivity and channel sharing. The second area deals with the automated management of the network and concentrates on issues such as link management and routing. The third area deals with the interface of the network to the users and some practical aspects of operating and maintaining a network.     

Connectivity properties of a packet radio network model

A model of a packet radio network in which transmitters with range R are distributed according to a two-dimensional Poisson point process with density D is examined. To ensure network connectivity, it is shown that πR²D, the expected number of nearest neighbors of a transmitter, must grow logarithmically with the area of the network. For an infinite area there exists an infinite connected component with nonzero probability if π R²D>N₀, for some critical value N₀. It is shown that 2.195<N ₀<10.526     

差分空时系统的天线选择算法

一般的天线选择算法都需要信道状态信息,根据信道参数选择天线.然而,估计多输入多输出(MIMO)系统的信道参数大大增加了系统复杂性,而且,在快衰落信道中,信道估计是很困难的.基于正交空时编码和接收信号向量的范数,提出了非相干的天线选择算法(NON-AS),不需要估计信道,并将算法应用于差分空时系统.性能分析和仿真结果表明,在高信噪比情况下,NON-AS算法能实现和完全复杂性系统同样的分集增益.     

Optimum transmission ranges in a direct-sequence spread-spectrummultihop packet radio network

The authors obtain the optimum transmission ranges to maximize throughput for a direct-sequence spread-spectrum multihop packet radio network. In the analysis, they model the network self-interference as a random variable which is equal to the sum of the interference power of all other terminals plus background noise. The model is applicable to other spread-spectrum schemes where the interference of one user appears as a noise source with constant power spectral density to the other users. The network terminals are modeled as a random Poisson field of interference power emitters. The statistics of the interference power at a receiving terminal are obtained and shown to be the stable distributions of a parameter that is dependent on the propagation power loss law. The optimum transmission range in such a network is of the form CK^α where C is a constant, K is a function of the processing gain, the background noise power spectral density, and the degree of error-correction coding used, and α is related to the power loss law. The results obtained can be used in heuristics to determine optimum routing strategies in multihop networks     

Optimizing information efficiency in a direct-sequence mobile packet radio network

We consider a direct-sequence multihop packet radio network using slotted ALOHA in a Rayleigh fading environment. We are interested in optimally choosing the transmission range, code rate, and slotted ALOHA transmission probability to be used by each node. We use a new performance measure, information efficiency, to analyze the network and show that the information efficiency of the low-cost mobile packet radio network can be improved approximately 20 fold by using the optimum parameters. We suggest a practical trellis-coded modulation scheme which comes close to realizing the theoretic limits found.     

天线选择对MIMO信道容量的影响

该文首先分析了多天线系统的信道容量,然后研究了当信道矩阵非满秩时,选择发射和接收天线对信道容量的影响。仿真试验结果表明,发射天线选择能提高系统容量,同时选择发射和接收天线虽然减小了复杂度和硬件成本,但对系统容量的增加低于单独进行发射天线选择时的情况。     

Spatial reuse in multihop packet radio networks

Multihop packet radio networks present many challenging problems to the network analyst and designer. The communication channel, which must be shared by all of the network users, is the critical system resource. In order to make efficient use of this shared resource, a variety of channel access protocols to promote organized sharing have been investigated. Sharing can occur in three domains: frequency, time, and space. This paper is mostly concerned with sharing and channel reuse in the spatial domain. A survey of results on approaches to topological design and associated channel access protocols that attempt to optimize system performance by spatial reuse of the communication channel is presented.     

TDM policies in multistation packet radio networks

A multistation packet radio network with m stations and a finite number of nodes n that uses a conflict-free protocol to access the backbone network of stations through a shared channel is discussed. The goal is to derive an allocation of the channel time slots (time-division multiplexing cycle), so that all transmissions will be conflict-free and some measure of performance (e.g., the expected total weighted throughput, the expected weighted holding cost) will be optimized. The methodology that is used is to bound the performance and to allocate the slots according to the golden ratio policy     

A transmit power control scheme for improving performance in amobile packet radio system

The problem of a number of mobile users attempting to send data packets over a commonly shared slotted channel to a central base station is studied. A scheme for controlling the transmit power of the mobiles is proposed and shown to yield better throughputs than a conventional transmit power scheme (in which all mobiles transmit with constant power) for both nonfading and fading channels. In any given time slot, mobiles that are closer to the base station are allowed to transmit at a higher power level in an attempt to improve capture probability