A spreading code protocol (GBCR protocol)suitable for DS CDMA wireless data networks is proposedin this paper. The network is co-ordinated by a centralstation (CS) which maintains a database tracking each user's status. Users are divided intogroups, each of which is assigned a “group-basedcommon” (GBC) code used by a transmitter in thegroup to acquire the current state of its target. Data communication is allowed only after apositive ACK packet from the CS is received by thetransmitter, so that all successful terminals aresheltered by the CS from possible third-partyinterference which may use the same receiver-based code.Analytical results reveal that the GBCR protocol caneffectively improve network stability andthroughput-delay performance.

The authors study a multiple chip-rate DS/CDMA system and its spreading code dependent performance. The multiple chip-rate technique is useful in some CDMA applications needing extra divisions among users in addition to code division to support variable data rate applications, such as multimedia systems. The study is applicable to both synchronous and asynchronous multiple chip-rate CDMA systems. A co-channel interference model based on correlation statistics for deriving bit error rate of a dual-chip-rate CDMA system is introduced considering various spreading codes, such as m-sequence, Gold, Gold-like, Kasami and Walsh codes. The results show that Gold code families are most suitable for the use in the dual-chip-rate CDMA system

The statistical correlation distribution convolution algorithm is introduced to study the performance of DS/CDMA indoor wireless systems. With the help of the algorithm, it is possible to obtain the bit error rate against number of simultaneous interfering transmitters, considering the effects of co-channel interference, Rayleigh multipath fading and power control schemes. The performance of two CDMA receivers, conventional correlator and equal-gain RAKE receiver, is compared. It is shown that the RAKE receiver can improve the system performance under the indoor multipath fading. However, its effectiveness under the power control is sensitive to the severity of multipath interference. When the multipath fading is rampant, a tight power control based on the main paths may not help improve the performance of the RAKE receiver.

Gordon-Mills-Welch (GMW) sequences possess a desirable two-valued autocorrelation function which helps a RAKE receiver track multipath returns. Unfortunately, their cross-correlation functions are less well controlled. Therefore, it is necessary to construct their subfamilies (taking advantage of its reasonably large family size) which offer satisfactory cross-correlation characteristics. The authors study several algorithms for constructing those quasi-optimal subfamilies in terms of minimised bit error rate under cochannel interference. The results show that performance of resultant subfamilies is very sensitive to the algorithms applied and subfamily sizes. A new criterion based on combined (even and odd) maximum cross-correlation is introduced for subfamily construction and two proposed highest-peak-deleting and most-peak-deleting algorithms are effective to construct the GMW quasi-optimal subfamilies.

This paper studies several algorithms for constructing quasi-optimal GMW subfamilies in terms of minimized bit error rate under co-channel interference. The results show that performance of resultant sub-families is very sensitive to the algorithms applied and sub-family sizes. A new criterion based on combinational (even plus odd) maximum cross-correlation is introduced for code selection and the resultant highest-peak-deleting and most-peak-deleting algorithms are effective to construct the GMW quasi-optimal sub-families.

The paper introduces a novel spreading code protocol, the adaptive group-receiver code protocol, offering flexibility and stability under varying traffic conditions. In the protocol, terminals are divided into groups co-ordinated by central stations and a group-based receiver spreading coding is used to manage the contention among users in the groups. The protocol can adaptively adjust the number of groups according to traffic load and throughput-delay requirements. The analytical results show that the protocol is particularly befitting for the applications in local wireless networks requiring high throughput and low access delay.

Either GMW sequence or m-sequence possesses a 2-valued auto-correlation function which helps to improve the performance of a RAKE receiver. However, their cross-correlation functions are less well controlled. Before they can be applied to a CDMA system, it is necessary to construct their sub-families (taking advantage of their large family size) which offer satisfactory cross-correlation functions. This paper studies several algorithms for constructing those quasi-optimum sub-families in terms of minimized bit error rate under cochannel interference. The study shows that the performance of resultant sub-families is sensitive to sub-family sizes and algorithms. A new criterion based on combined (even and odd) maximum cross-correlation for code selection is introduced, and highest-peak-deleting and most-peak-deleting algorithms are suggested for constructing quasi-optimum sub-families of GMW and m-sequences.

Some CDMA systems serve a finite number of simultaneously active users. Thus, its performance is spreading code dependent and Gaussian approximation is not appropriate to evaluate its performance. To choose proper spreading codes for a finite CDMA system, both peak cross-correlation and squared-sum of cross-correlations should be considered. An algorithm based on multiple variable Bernoulli process is introduced to evaluate the BER due to co-channel interference. The algorithm is useful for spreading code dependent capacity analysis, regardless of the CDMA system size and operation. The results show that small Kasami and Gold (1968) like codes offer a high capacity in a finite CDMA system.

This paper studies several algorithms for constructing quasi-optimal m-sequence subfamilies in terms of minimized BER under co-channel interference. The results show that the performance of resultant sub-families is sensitive to the sub-family sizes and the algorithms employed. A new criterion based on combinational (even plus odd) maximum cross-correlation for the code selection is introduced, based on which both highest-peak-deleting and most-peak-deleting algorithms are effective to construct the quasi-optimal subfamilies

GMW sequence possesses desirable 2-valued auto-correlation functions however with less well controlled cross-correlation functions. This paper studies several algorithms for constructing those quasi-optimal sub-families in terms of minimized bit error rate under co-channel interference. Performance of resultant sub-families is very sensitive to the algorithms and sub-family sizes. A new criterion based on combinational (even plus odd) maximum cross-correlation is introduced for code selection and the resultant highest-peak-deleting and most-peak-deleting algorithms are effective

A DS/CDMA system may use multiple chip rate to support multi-data rate services and provide extra divisions among users. The technique is called ''code & chip rate division multiple access (C(2)RDMA)'' its BER and performance for a two-chip rates system is analyzed. Two methods (using co-channel interference Bernoulli model and Gaussian approximation) are compared. The results show that C(2)RDMA performs well for both small and large sized systems, particularly when a parallel correlator is employed for the lower chip-rate receivers. Various spreading code families such as M-sequence, Gold/Gold-like code, Kasami code and Walsh code are compared as well.

A new quadrature-overlapped modulation (QOTRC modulation) with a quasi-constant envelope is proposed in this paper. The new modulation possesses fast-decayed spectral side lobes. Bandwidth efficiency and detection efficiency of the new modulation under coherent detection over a band-limited non-linear satellite channel are studied and compared with those of MSK (a constant-envelope modulation) and SQORC (staggered quadrature-overlapped raised-cosine) modulations. The results obtained in this paper show that the new modulation can offer a satisfactory bit error rate (BER), which is comparable to or even better than that of MSK and much better than that of SQORC (a previously reported quadrature-overlapped modulation), depending on the signal-to-noise ratios (SNRs) and system bandwidth.

A new scheme to study the performance of a DS/CDMA indoor wireless system, the correlation statistics distribution convolution (CSDC) modeling, is introduced in this paper. With the aid of the CSDC modeling, the hit error rate versus number of simultaneous interfering transmitters can be directly evaluated, considering the effects of Rayleigh fading, power control, multipath and co-channel interference. The performance of two CDMA receiver structures, conventional correlator and RAKE receiver. is compared, It is shown that the RAKE receiver is effective in improving the system performance under indoor multipath fading. However. its effectiveness under transmitter power control is sensitive to the severity of multipath interference in the indoor channel. When the multipath fading is severe, a tight power control over the main paths may not be able to improve the performance of the RAKE receiver.

In the paper a spreading code protocol (the code-sensing R(3) code protocol) designed for wireless local networks is proposed and its performance is analysed. In a network adopting the protocol, destructive collisions among terminals are minimised by utilising the busy code-sensing and dual chip-rate techniques in transmissions of the REQ and ACK/data packets. A two-dimensional continuous-time Markov model is applied to study the behaviour of the protocol. The results show that a respectable improvement in throughput-delay performance can be achieved by the proposed protocol when compared to those previously reported in the literature.

A spreading code protocol (GBCR protocol) suitable for CDMA (packet radio) wireless data networks is proposed. The network is coordinated by a central station which maintains a database tracking each user's status. Users are divided into groups, each of which is assigned a “group-based common” code used by a source terminal to consult the central station for a destination status. Analytical results show that the proposed protocol can effectively improve network stability and throughput/delay performance

The code protocol (the R3 protocol) for DS/SSMA wireless data networks is examined further and an analytical method is given of studying its delay and throughput bounds. In this protocol the communication-initiation process terminals uses handshaking packets (REQ and ACK packets), followed by the data packet. Different chip rates are utilised in transmissions of different packets to avoid destructive collisions between them. All packets are encoded by receiver-based codes. It is shown that the throughput lower bound of this protocol is about 0.24 when the normalised offered channel-traffic load is equal to one, and that the protocol offers stability to the network even at a very high offered channel-traffic load.

A novel quadrature-overlapped modulation with a quasiconstant envelope is presented and studied in the paper. Its performance with coherent detection over band-limited nonlinear satellite channels is compared with MSK and QORC modulations. The results show that the new modulation possesses an ideal BER performance very close to that of MSK (constant-envelope modulation) and much better than that for QORC. In addition, the side lobes of its transmitting signal spectrum roll off very fast.

The code sensingR3 code protocol designed for wireless data networks is proposed and its performance is analysed in this paper. The communication between two terminals is initiated by hand-shaking packets (the REQ and ACK packets), followed by data packet transmission. The destructive collisions among terminals are avoided by utilising busy code sensing and chip-rate division multiple access (CRDMA) techniques in transmissions of the REQ packet and the data packet (or ACK packet). A two-dimensional continuous-time Markov model is used to analyse the behaviour of the network. Analytical results are given which show that a remarkable improvement in throughput-delay performance can be achieved by the proposed protocol when compared to those for other reported protocols.

To relieve the contention in packet initiations in CDMA packet radio networks, a novel protocol, the busy code broadcasting and sensing protocol, is proposed, and its steady-state throughput-delay performance upper bounds are numerically analysed. The results reveal that a high throughput of about 0.47 (when the normalised channel traffic r = 1) and a stable performance of the network can be achieved by busy code broadcasting and sensing to avoid possible packet conflicts in the CDMA packet radio channel. The hidden terminal problem which exists in carrier sense multiple access is avoided in the proposed protocol. The study also shows that the new protocol can use CDMA spreading codes more efficiently than can other conventional spreading code protocols.

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 the R code sensing protocol is developed to evaluate its steady-state performance.<>