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.
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.
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.
Multiple chip rates can be applied to a DS/CDMA system in order to enhance the potential system capacity which otherwise is limited by the spreading code family size. The technique is called “chip rate division access” (CRDMA). A co-channel interference method based on cross-correlation statistics is used to study the performance of the CRDMA with various spreading code families
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
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.
In this paper, a novel multiple access scheme, chip rate division multiple access (CRDMA), based on CDMA is proposed. This helps to increase the capacity of a CDMA system by dividing users not only by different codes but also by different chip rates. Both synchronous and asynchronous CRDMA systems are considered in this paper. A method based on cross-correlation level statistics to analyze the BER of an asynchronous CDMA/CRDMA system is introduced and the performance for both CRDMA and normal CDMA systems using various orthogonal code families, such as M-sequences, Gold, Gold-like, Kasami and Walsh codes, is compared.
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.
GMW and m-sequences possess 2-valued auto-correlation function but their crosscorrelation functions are not well controlled. This paper studies algorithms constructing their quasi-optimal sub-families. The results show that both highest-peak-deletmg and most-peak-deleting algorithms are effective in terms of minimized bit error rate under COchannel interference.
In a situation such as a traffic accident on a highway, the active mobiles in an affected cell may easily outnumber the capacity, and an excessive increase in CDMA noise may, in the worst case, block all calls in the cell if the users insist on calling through the same cell site. A scheme to alleviate such congestion in CDMA cellular systems is proposed, so that traffic load is adaptively shed from affected cells by forced hand-offs of the mobiles farthest away from current cell site. The capacity with adaptive load shedding is studied by computer simulations considering two scenarios: a single congested cell with six neighbouring cells partially loaded, and three consecutive congested cells with four neighbouring cells partially loaded. The results show that the scheme offers higher CDMA cellular capacity gain than the normal power-up control adopted by the current CDMA cellular standard.
An unslotted DS/SSMA packet-radio protocol (the triple-receiver-based code (R3) protocol) suitable for code-division multiple-access (CDMA) wireless data networks is proposed. The communication between two data terminals is initiated by hand-shaking (request and acknowledgement stages) followed by data-packet transmission (pair-up stage), using the receiver-based signature codes for multiple-accessing. The two-dimensional continuous-time Markov chain was used to model and analyse the behaviour of the network. The analytical results show that a respectable improvement in throughput-delay performance can be achieved, applying the proposed protocol to unslotted DS/SSMA packet-radio networks, when compared to other reported code protocols
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 new collision-avoiding protocol, the receiver-and-transmitter (R&T) code-sensing protocol, is formulated and its performance upper bounds are numerically analyzed. The results reveal that a high throughput and a stable performance of a distributed code-division multiple-access (CDMA) packet radio network can be achieved by broadcasting both transmitter and receiver codes into the shared CDMA channel to avoid possible packet conflicts. To measure the efficiency of the orthogonal codes used, the effective code utilization (ECU), defined as the ratio between the throughput and code consumption, is introduced and evaluated. The evaluation shows that the R&T code-sensing protocol has an ideal ECU.<>
The authors suggest a new algorithm for binary coding waveform sidelobe reduction after matched filtering and present a general method by which optimized sidelobe suppression filters for Barker codes can be obtained with a peak output sidelobe 2.62 dB lower than the results found in the literature (for 13-b Barker code). This optimization algorithm is also promising for other binary coding waveforms, such as truncated pseudonoise (PN) sequences and concatenated codes. This new approach can readily be applied to sidelobe-reduction filter design for other binary coding waveforms, such as truncated PN sequences, concatenated codes, etc., which often find their applications in radar systems and spread spectrum communication systems.
