Optimum packet size for data communications

If packets of data carry D message bits and H header bits and reliable estimates of message length are not available, then D should be chosen to be about eight times greater than H in order to obtain maximum throughput for a given transmission rate.     

Principles and lessons in packet communications

After nearly a decade of experience, we reflect on the principles and lessons which have emerged in the field of packet communications. We begin by identifying the need for efficient resource sharing and review the original and recurring difficulties we had in achieving this goal in packet networks. We then discuss various lessons learned in the areas of: deadlocks; degradations; distributed control; broadcost channels; and hierarchical design. The principles which we discuss have to do with: the efficiency of Large system; the switching computer; network constraints; distributed control; flow control; stale protocols; and designers not yet experienced in packet communications. Throughout the paper, we identify various open issues which remain to be solved in packet communications.     

Wavelet packet modulation for wireless communications

As proven by the success of OFDM, multicarrier modulation has been recognized as an efficient solution for wireless communications. Waveform bases other than sine functions could similarly be used for multicarrier systems in order to provide an alternative to OFDM. In this paper, we study the performance of wavelet packet transform modulation (WPM) for transmission over wireless channels. This scheme is shown to be overall quite similar to OFDM but with some interesting additional features and improved characteristics. A detailed analysis of the system's implementation complexity as well as an evaluation of the influence of implementation‐related impairments are also reported. Copyright © 2004 John Wiley & Sons, Ltd.     

Cellular digital packet data network

Cellular digital packet data (CDPD) is a data network designed to meet growing mobile data transmission needs. CDPD networks can stand alone or overlay on the cellular voice system by drawing radio resources from the pool of unused or free cellular analog voice channels. Detection as to whether a channel is free or occupied is mechanized through channel sniffers. Once the CDPD network seizes a channel, it continues to use the channel as long as it is free and leaves the channel within 40 ms of initiation of any voice activity on the channel-the CDPD network then hops to another free channel, if available. CDPD follows slotted nonpersistent digital-sense multiple access with collision detection (DSMA/CD). In addition, it performs channel-error detection and channel-error recovery. We investigate several aspects of the CDPD network, namely, the: (1) effect of CDPD on cellular voice and (2) the delay-throughput performance due to DSMA/CD with error detection     

Multichannel reservation protocol for packet multiple-access communications

An efficient protocol well suited for the transmission of variable length messages over a group of parallel channels is described. The protocol is applicable to star networks with inbound multiple-access and outbound broadcast channels. Throughput capacity of the inbound channels is analysed and optimised with respect to message length and packet overhead.<>     

Capture-division packet access for wireless personal communications

This paper presents a new architecture for the third-generation mobile systems, capture-division packetized access (CDPA), that overcomes most of the limitations of present cellular systems. It addresses the three main issues of radio access, namely the channel reuse, the multiple access, and the handover problems, in complete adherence to packet-switching principles. The CDPA channel reuse mechanism is a completely new alternative with respect to time-division, frequency-division, or code-division multiple-access (TDMA, FDMA, and CDMA, respectively), which achieve communication parallelism by subdividing the bandwidth a priori among cells. In CDPA, a single frequency channel is used and parallel transmissions are achieved through the “capture” capability of receivers. The hybrid reservation-polling multiple access mechanism used in CDPA is able to integrate any kind of traffic and guarantees almost immediate retransmission of packets that are not captured, thus assuring their correct reception. Finally, the packet-switching approach allows connectionless communications with any base station (BS), and eliminates the need for extra radio traffic in managing handovers. This turns out to be very effective in local area systems where the required high bandwidth is obtained by using a pico-cell structure. We present the CDPA architecture, discuss some implementation issues, and evaluate its performance under a variety of system parameters and operating conditions, using analytical and simulation methods     

Cellular communications using aerial platforms

This paper is devoted to the study of cellular communications using aerial platforms (APs). A set of key equations is derived that quantify the coverage area on the ground as a function of AP elevation, the operation of the adaptive multibeam antenna on the AP, and the formulation of contiguous terrestrial cells and their shapes. Specifically, we consider the deployment of an AP to provide terrestrial mobile radio communications using the universal mobile telecommunication system operating in its wide-band code-division multiple-access mode. Calculations are made of the number of users versus E_b/N₀ for different service rates. Multitiered cellular structures having cells of different size that are steerable with the offered teletraffic are examined. The array structure to achieve this is identified. The preliminary results shows that an AP at a height of 21 km covers an area of radius 517 km. Up to 21 users per cell with a service rate of 8 kb/s can be accommodated in the 3.2-GHz band. These services can be provided within an area of radius 70 km with transmitted powers of less than 1 W. High system capacity is proved to be possible by constructing cells of radius as small as 100 m using square planar arrays with dimensions of less than 12 m ×12 m. The AP system provides high capacity and Doppler frequency shifts that only originate from roving mobiles     

Optimum VoIP packet routing using a communications processor

This article presents a new architecture for the VoIP media gateway using only a communications processor and digital signal processors. The new architecture can be used by telecommunications equipment manufactures to replace a network processor and a general-purpose processor with a single communications processor, thereby can reduce the system cost, power consumption, printed circuit board (PCB) area, software complexity and time to market. In the new architecture the modules are interconnected via Ethernet interfaces, which make voice packet encapsulation possible in digital signal processors. This relieves the network processor, which in voice over IP (VoIP) media gateways is most commonly used for the routing of VoIP packets and voice-packet encapsulation, and means it can be replaced by a communications processor. The presented media gateway architecture makes it possible to combine the data- and control-plane application on a single-communications processor, but only in the case of a properly optimized program code and an optimized Ethernet driver. Therefore, the main part of the article is dedicated to a presentation of the methodology for the analysis and optimization of the presented systems. In order to support this methodology, a new tool named performance monitor (PM) was developed. The PM tool is presented here, and was used for optimizing the Ethernet driver. The Ethernet driver was optimized and modified in such a way as to put a minimal load on the microprocessor core of the communications processor when routing the VoIP packets to digital signal processors and back. The article ends with a presentation of the experimental optimization results, which were acquired from a real telecommunications system.     

Data-link packet dropping models for wireless local communications

Packet dropping statistics is studied for three data-link retransmission schemes, where packets are dropped at the transmitter due to: (1) buffer overflow; (2) too many transmission attempts; and (3) excessive delay. An analytical framework for the computation of the complete statistics of the dropping process and of the delay is presented and some numerical results are discussed. In particular, the dropping properties of the three different schemes are compared. The channel model considered takes into account correlated errors as occur in the wireless environment     

QoS-oriented packet scheduling for wireless multimedia CDMA communications

In the third-generation (and beyond) wireless communication systems, there will be a mixture of different traffic classes, each having its own transmission rate characteristics and quality-of-service (QoS) requirements. In this paper, a QoS-oriented medium access control (MAC) protocol with fair packet loss sharing (FPLS) scheduling is proposed for wireless code-division multiple access (CDMA) communications. The QoS parameters under consideration are the transmission bit error rate (BER), packet loss, and delay requirements. The MAC protocol exploits both time-division and code-division statistical multiplexing. The BER requirements are guaranteed by properly arranging simultaneous packet transmissions and controlling there transmit power levels, whereas the packet loss and delay requirements are guaranteed by proper packet scheduling. The basic idea of FPLS is to schedule the transmission of multimedia packets in such a way that all the users have a fair share of packet loss according to their QoS requirements, which maximizes the number of the served users under the QoS constraints. Simulation results demonstrate effectiveness of the FPLS scheduler, in comparison with other previously proposed scheduling algorithms.     

Cellular digital packet data: channel availability

Cellular digital packet data (CDPD) networks borrow idle radio channels from advanced mobile phone standard (AMPS) cellular networks to send packet data traffic. We explore the amount of unused AMPS capacity available to parasitic data networks such as CDPD. Due to trunking inefficiencies, a relatively large amount of spare AMPS airlink capacity can be found. In addition, the periods of time AMPS channels are idle are fairly long. Due to fluctuations in the number of AMPS channels in a sector busy serving AMPS calls, there will be periods of time when there is not an ample number of idle AMPS channels for CDPD. Resource contention between CDPD and AMPS will affect the amount of data that can be carried on the CDPD airlink and the performance of higher layer protocols. We present analytical results which serve as the basis for cell site capacity engineering rules for CDPD networks     

Commercial, legal, and international aspects of packet communications

Packet switching technology emerged rapidly in the 1970's as another viable mode of communications switching, along with circuit and message switching. Since packet switching offers economical and versatile data communication capabilities in a multiuser environment, it is particularly well suited for furnishing public data communication network services. Public packet networks are now established or being developed in most industrialized countries, and the introduction of these networks has raised policy issues relating to the structure and regulation of the national networks, and the interconnection of national networks into an international packet switching system. This paper reviews these issues and concludes that public packet switching network services will continue to be regulated in all cases; that competitive packet networks will coexist in the U.S. and in Canada, but that only one national packet network will exist in each of most other countries; that packet networks will aggravate the problem of distinguishing nonregulated data processing services from regulated data communication services; that international interconnection of public packet networks based upon CCITT standanh will occur rapidly over the next several years; and that a unified international packet switching system will eventually emerge similar to today's international telephone and telex systems.     

Optimal packet length for wireless communications using reconfigurable intelligent surfaces

Telecommunication Systems - Reconfigurable intelligent surfaces (RIS) allow significant throughput enhancement as all reflections have the same phase at the receiver. In this paper, we suggest to...     

Modelling and performance of packet synchronization in A data communications system

This paper deals with some problems of packet synchronization in a slotted packet-radio communications system. The problems considered are bit-synchronization and unique word detection for bursty systems. The necessary overhead for synchronization purposes is dimensioned for applications in land-mobile satellite communication systems. The performance of synchronization is evaluated using hardware measurement equipment, including a commercial bit-synchronizer. Using these results, the performance loss of communication systems due to packet synchronization effects can be estimated. This is done for the additive white Gaussian noise channel and the class of land-mobile satellite channels.     

C-PRMA: a centralized packet reservation multiple access for localwireless communications

Packet-switched technology has been demonstrated as effective in cellular radio systems with short propagation delay, not only for data, but also for voice transmission. In fact, packet voice can efficiently exploit speech on-off activity to improve bandwidth utilization over time division multiple access (TDMA). Such an approach has been first suggested in the packet reservation multiple-access (PRMA) technique, an adaptation of the reservation ALOHA protocol to the cellular environment. However, being PRMA-based on a fixed frame scheme, it cannot thoroughly take advantage of the very short propagation delays encountered in microcellular systems that allow, for instance, the immediate retransmission of packets lost because of the interference noise from adjacent cells. We present the centralized PRMA, a natural enhancement of PRMA, in which the base station (BS) plays a central role in scheduling the transmissions of mobile stations (MSs). As a consequence, the transmission scheduling is very flexible and can account for the different traffic rate and delay constraints that emerge from voice and data integration. A packet retransmission policy to recover corrupted packets can be implemented and operated efficiently to provide an acceptable grade of service, even in a very noisy environment. The simulation results presented show the quantitative improvements of the centralized packet reservation multiple-access (C-PRMA) performance with respect to PRMA     

全国公用无线数据网(CDPD)

介绍了无线数据网（ＣＤＰＤ）的基本概念和工作原理,系统特点和系统组成以及应用范围,并介绍了ＣＤＰＤ一期工程在我国实施情况。     

Anti-frequency-shift packet detection for D2D power-saving communications over Wi-Fi network

An efficient packet detection scheme based on Wi-Fi interface was proposed.It was implemented by employing a novel normalized factor as a denominator in OFDM symbol synchronization-timing metric.Compared to the old-tradition schemes,the proposed scheme can not only obtain great detection probability,but also achieve the threshold setting without pre-estimation of frequency offset.Both theoretical analysis and conducted simulation results show that the new scheme facilitates threshold selection for a wide range of signal-to-noise ratio (SNR) in additive white Gaussian noise (AWGN) channel.Besides,the threshold setting in multi-path Rayleigh fading channels can be determined according to the AWGN case straight forwardly.     

A call admission control scheme for packet data in CDMA cellular communications

In wireless cellular communication systems, call admission control (CAC) is to ensure satisfactory services for mobile users and maximize the utilization of the limited radio spectrum. In this paper, we propose a new CAC scheme for a code division multiple access (CDMA) wireless cellular network supporting heterogeneous self-similar data traffic. In addition to ensuring transmission accuracy at the bit level, the CAC scheme guarantees service requirements at both the call level and the packet level. The grade of service (GoS) at the call level and the quality of service (QoS) at the packet level are evaluated using the handoff call dropping probability and the packet transmission delay, respectively. The effective bandwidth approach for data traffic is applied to guarantee QoS requirements. Handoff probability and cell overload probability are derived via the traffic aggregation method. The two probabilities are used to determine the handoff call dropping probability, and the GoS requirement can be guaranteed on a per call basis. Numerical analysis and computer simulation results demonstrate that the proposed CAC scheme can meet both QoS and GoS requirements and achieve efficient resource utilization.     

High data-rate packet communications for cellular networks usingCDMA: algorithms and performance

The advantages of code division multiple access (CDMA) for cellular voice have become well known, and IS-95-based systems have now been widely deployed. Attention is now focused on higher data-rate packet services for cellular systems. Although many packet multiple access schemes have been studied over the years, researchers have often studied single cell performance and ignored reuse. Moreover, direct sequence spread spectrum (DSSS) has been considered unsuitable for high data-rate packet multiple access since spreading limits the permitted data rates, DSSS requires large overhead (preambles) for acquisition and requires closed-loop power control. In this paper, we describe a scheme for high data-rate packet service using CDMA that addresses all of the above problems and has been standardized in Revision B of IS-95. A low rate fundamental code channel is maintained that eliminates the need for long preamble and provides closed-loop power control. Reuse is managed by the infrastructure through a “burst-level” admission control based on load and interference-level measurements at the base stations and mobiles. We report on the feasibility of such a burst-mode packet data service for cellular CDMA networks. The focus is not only on the performance of high data-rate users, but also on the impact on voice users sharing the CDMA band. We propose a multitiered performance analysis methodology consisting of a mix of static simulations, dynamic simulations at different time scales, and analytic methods to address the various feasibility issues: impact on coverage; capacity; power control; and effectiveness of burst admission algorithms. Based on the current study, we can conclude that the proposed approach is well suited for third-generation wideband CDMA systems being considered for standardization throughout the world