摘要:

In some applications, such as slotted indoor CDMA communications, where the network performance depends mainly on periodic crosscorrelation functions of spreading codes, minimisation of the peak crosscorrelation level (CCL) is not a sufficient measure to ensure an optimal performance. The occurrence frequency of CCLs is introduced as another important parameter to judge CDMA code families. The 4-CCL and 5-CCL code families which possess more ideal OFs of CCLs than the Gold code are presented. A new technique using a multivariable Bernoulli process to model the outputs of a CDMA receiver is developed to evaluate the network level BER performance in a slotted system. The results obtained show that the 4-CCL and 5-CCL codes obviously outperform the Gold code in the BER performance.

DOI:10.1049/ip-i-2.1992.0011

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Packet conflicts in an asynchronous distributed CDMA packet radio network is a main cause of throughput inefficiency and network instability. To reduce the packet conflicts due to random packet initiations in the network an alternative collision-avoiding CDMA protocol, the receiver-based (R) spreading code sensing protocol, is proposed and its performance is numerically analysed. The results reveal that, by using the code-sensing technique in the conventional receiver-based spreading code protocol, the throughput-delay performance and the stability of the network can be dramatically improved. The results are also compared with those of other CDMA spreading code protocols without code sensing. A two-dimensional time-continuous Markov chain model for theRcode sensing protocol is developed to evaluate its steady-state performance.

DOI:10.1049/ip-i-2.1992.0012

出版商:IEE    

年代:1992

数据来源: IET

摘要:

A recent second generation highcapacity mobile radio telephone system in Japan employs selection diversity with two branches on the mobile receiver to counteract co-channel interference from distant base stations operating with identical frequencies. From an actual point of view it seems more reasonable to assume that the fluctuations of signal carrier envelopes on the mobile receiver are approximated by them-distribution proposed by Nakagami when we try to investigate fading statistics for land mobile radio not only in urban areas but in suburban or open areas. Them-distribution is a generalisation of the Rayleigh distribution and it can take account of the influence of a superimposed specular component other than scattered and reflected waves. The probability density function of the wanted signal envelope and its characteristic function for selection diversity in them-fading channel are derived in conveniently closed form, and the probability of co-channel interference that the wanted signalcarrier to interference power ratio (CIR) is less than a specified protection ratio is calculated. The results obtained will serve to decide the modulation system employed and to estimate the frequency re-use distance, the number of channel groups, and the efficiency of spectrum use in cellular mobile radio.

DOI:10.1049/ip-i-2.1992.0013

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The paper is concerned with the bit error rate (BER) performance of multiple hops/ symbol fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) systems operating through an indoor radio multipath Rayleigh fading channel. M-ary frequency-shift-keying (MFSK) modulation with noncoherent square-law envelope demodulation and Reed-Solomon (RS) coding is considered. Results obtained in this study show that an FFH-SSMA system is not sensitive to the changes in the number of paths. Employing RS coding with an increased numberMof MFSK signals yields a significant improvement in BER performance. Assuming a given system bandwidth, using a single hop per symbol is the best solution when the multiaccess interference can be large. Using several hops per symbol is more advantageous when the multiaccess interference is small.

DOI:10.1049/ip-i-2.1992.0014

出版商:IEE    

年代:1992

数据来源: IET

摘要:

CSMA/CD networks (or Ethernets) have become the standard of networking in many medium- to large-scale establishments such as universities, research laboratories and hospitals. However, many departments of these establishments are reluctant to transmit into these networks sensitive information such as examination papers and student records in universities, technical data in research laboratories, or patient records in hospitals. This is due to the fact that all data transmitted into a CSMA/CD network can be received by any station with its network access controller programmed into the promiscuous mode. The paper presents a hardware-oriented security scheme for the physical layer of CSMA/CD networks. In the scheme, connection and data confidentiality in CSMA/CD networks are achieved while the broadcast nature of the networks is preserved. The basic security mechanism is the encipherment of CSMA/CD frames transmitted from CSMA/CD controllers. This mechanism is implemented in a security controller inserted between a CSMA/CD controller and its transceiver. In developing the security key management mechanism in the security controller, a key number (or key reference) concept was introduced. With this new key number concept, the distribution of session keys, either by a key exchange or a key distribution centre, becomes unnecessary. The security scheme allows communications in either normal or security,mode; however, stations without the security controller can only receive frames transitted in the normal mode. Apart from the additional security controller, hardware and software alterations are not required to implement the security scheme in any existing CSMA/CD networks.

DOI:10.1049/ip-i-2.1992.0015

出版商:IEE    

年代:1992

数据来源: IET