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We consider a hybrid direct-sequence frequency-hopped (DS/FH) code division multiple access (CDMA) communication system, where the transmission power and data rate are adapted relative to the channel variation. Instead of random frequency hopping, hopping pattern is adaptively adjusted to obtain the maximum channel gain among available frequency slots. Transmission power and/or data rate are also adapted such that a target transmission quality is maintained. It is shown that the proposed scheme provides a higher average data rate than pure DS/CDMA with power and rate adaptations, subject to the identical average transmission power and bandwidth constraints.

We investigate a generalized combined power and rate adaptation scheme in direct-sequence (DS) code-division multiple-access (CDMA) communications over Nakagami fading channels. The transmission power allocated to user i is proportional to , where is the channel gain of user i and p is a real number, and the data rate (i.e., spreading gain) is jointly adapted so that a desired QoS is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme provides a significant performance improvement over power-only and rate-only adaptation.

We propose an efficient frequency-time domain resource allocation scheme in multi-carrier (MC) direct-sequence code-division multiple-access (DS/CDMA) communications. We consider, as a power allocation strategy in the frequency domain, transmitting each user`s DS waveforms over the user`s sub-band with the largest channel gain. We then consider rate adaptation in the time domain, where the data rate is adapted such that a desired transmission quality is maintained. We analyze the achievable average data rate of the proposed scheme with fixed average transmission power, and compare the performance to single carrier DS/CDMA systems with power and rate adaptations.

We consider power and rate adaptations in multicarrier (MC) direct-sequence code-division multiple-access (DS/CDMA) communications under the assumption that channel state information is provided at both the transmitter and the receiver. We propose, as a power allocation strategy in the frequency domain, to transmit each user's DS waveforms over the user's sub-band with the largest channel gain, rather than transmitting identical DS waveforms over all sub-bands. We then adopt channel inversion power adaptation in the time domain, where the target user's received power level maintains at a fixed value. We also investigate rate adaptation in the time domain, where the data rate is adapted such that a desired transmission quality is maintained. We analyze the BER performance of the proposed power and rate adaptations with fixed average transmission power, and show that power adaptation in both the frequency and the time domains or combined power adaptation in the frequency domain and rate adaptation in the time domain make significant performance improvement over the power adaptation in the frequency domain only. We also compare the performance of the proposed power and rate adaptation schemes in MC-DS/CDMA systems to that of power and rate adapted single carrier DS/CDMA systems with RAKE receiver.

We consider transmission power adaptations in multicarrier code-division multiple-access communications, where the transmission power is adapted in frequency and/or time domain in response to channel variations. With frequency-domain power adaptation, we propose to allocate the transmission power over N' (1 les N' les N) strongest subcarriers (which have the highest channel gains) rather than over all possible N subcarriers. We examine the effect of choosing N' on the performance of the frequency-domain power adaptation scheme and find that there exists an optimal N' that minimizes the average bit error rate (BER). In the time domain, we consider adapting the transmission power so that the desired signal strength at the receiver output remains at a fixed level. We analyze the BER performances of frequency-, time-, and combined frequency-time-domain power adaptations with an average transmission power constraint. Our results show that the frequency-and time-domain power adaptation schemes outperform the nonadaptive (i.e., constant uniform power over all subcarriers) scheme, particularly for the noise-and interference-limited regions, respectively. The combined frequency-time-domain power adaptation is shown to have a significant performance gain over the power adaptation in only the frequency or time domain, as well as over the nonadaptive scheme. We also present numerical results to investigate the effect of channel estimation error on the performance of the proposed power adaptation schemes.

In this paper, we propose an adaptive data transmission scheme for DS/CDMA packet radio communication systems in bandlimited indoor multipath fading channels. We first analyze the relationship between the code rate and the processing gain (defined as the number of chips per coded bit) in maximizing the normalized throughput in connection with the channel state of the indoor multipath fading channels. One observation made is that the maximum throughput with BPSK modulation is attained when the code rate is chosen as low as possible irrespective of the channel state, and the processing gain is increased (decreased) as the channel becomes worse (better). The other observation made is that when DPSK modulation is employed, there exists an optimal combination of the code rate and the processing gain in maximizing the normalized throughput for each channel state. Based on these observations, we propose to adapt the processing gain and/or code rate according to the fading conditions in order to maximize the normalized throughput. We analyze the performance of the proposed scheme and compare it with the non-adaptive data transmission scheme. Our results show that the adaptive transmission scheme yields a significant performance improvement over the nonadaptive scheme, and increasing the adaptation level is more effective as the channel gets worse, but the 3-state adaptation seems to be practically optimum.

We consider a hybrid direct-sequence frequency-hopped (DS/FH) code division multiple access (CDMA) communication system, where the transmission power, data rate (i.e. spreading gain), and hopping frequency are adapted relative to the channel variations. Instead of random frequency hopping, hopping pattern is adaptively adjusted to obtain the maximum channel gain among available frequency slots. Transmission power and/or data rate are also adapted such that a target transmission quality is maintained. It is shown that the proposed scheme provides a higher average data rate than pure DS/CDMA with power and rate adaptations, subject to the identical bandwidth and average transmission power constraints.

We investigate the optimal chip rate of power or rate adapted direct-sequence code division multiple access (DS/CDMA) communication systems in Nakagami fading channels. We find that the optimal chip rate that maximizes the spectral efficiency depends upon both the channel parameters, such as multipath intensity profile (MIP) and line-of-sight (LOS) component, and the adaptation scheme itself. With the rate adaptation, the optimal chip rate is less than 1/T m irrespective of the channel parameters, where T m is multipath delay spread. This indicates that with the rate adaptation, correlation receiver achieves higher spectral efficiency than RAKE receiver. With the power adaptation, however, the optimal chip rate and the corresponding number of tabs in RAKE receiver are sensitive to MIP and LOS component.

In this paper, power adaptation for direct-sequence code-division multiple-access communications that employs a successive interference cancellation (SIC) receiver is considered. The transmission power is adapted so that, with the channel variations, the received power levels of each user have appropriate disparities. Under the constraint of average transmission power, we consider two strategies in adjusting the disparity between received signal powers. With the first strategy, the average bit-error rate (BER) for a given user averaged over channel fading statistics is minimized, while with the other, the instantaneous BER is equal for all users. We find that the performance difference between the two strategies becomes negligible as the average transmission power or line-of-sight component increases. We also discuss the impact of appropriate disparity in received power levels on the BER performance of SIC receivers.

We consider combined rate and power adaptations in direct-sequence code-division multiple-access communications, where the transmission power and the data rate are adapted relative to channel variations. We discuss the power gain that the combined adaptations provide over power adaptation. Then, we consider an integrated voice and data transmission system that offers a constant bit rate voice service, using power adaptation and a variable bit rate data service with rate adaptation. We present an expression for the required average transmission power of each traffic type having different quality-of-service specifications and discuss the capacity gain over power adaptation for voice and data.

Since code-division multiple-access (CDMA) systems are interference limited, interference managements in terms of power control and interference cancelation have been investigated extensively in the past. In this paper, we consider a power control scheme for CDMA communications with successive interference cancelation (SIC). The proposed scheme is to make the received power levels be geometrically distributed such that the average BER after cancelation, averaged over all users, can be minimized. We show that the performance of the proposed scheme is significantly improved over existing power control schemes.

We consider combined rate and power adaptation schemes in direct-sequence code division multiple access (DS/CDMA) communications, where the transmission power and the data rate are jointly adapted relative to channel variations. We propose to allocate the transmission power proportional to \(G_i^p\), where G i is the channel power gain and p is a real number, and to adapt the data rate simultaneously so that a desired transmission quality is maintained. We analyze the average data rate of the proposed adaptation scheme, and show that the proposed joint adaptation scheme provides up to 3.7–5.4 and 1.5–3.2 dB of power gains over power only adaptation and rate only adaptation, respectively, when peak-to-average power ratio is 2 to 10, in a Rayleigh fading channel with δ = 0.5, where δ is the decaying exponent of multipath intensity profile (MIP).

We propose a multicarrier code-division multiple-access (MC-CDMA) system with adaptive transmission power allocation. The transmission power is allocated over M′ strongest subcarriers among M available ones. Using only M′ subcarriers of which channel gains are relatively large indicates that the transmission power to maintain the desired received signal strength can be reduced, but decreasing M′ also lead to a reduction of effective spreading gain to mitigate the multiple access interference. We analyze the trade-off between M′ and effective spreading gain, and find the optimal M′ that minimizes the average bit error rate (BER). Our results show that the BER can be significantly reduced if M′ is properly chosen, and transmit signals over only the strongest subcarrier (M′=1) is the best especially for low SNR regions.

We study the optimal chip rate of adaptive power and rate direct-sequence code division multiple access (DS/CDMA) communication systems in Nakagami fading channels. We find that the optimal chip rate that maximizes the spectral efficiency depends upon both the channel parameters, such as multipath intensity profile (MIP) and line-of-sight (LOS) component, and the adaptation scheme itself. With the rate adaptation, the optimal chip rate is less than 1/T m irrespective of the channel parameters, where T m is multipath delay spread. With the power adaptation, however, the optimal chip rate and the corresponding number of tabs in RAKE receiver are function of the MIP and the LOS component.

We present a joint power and rate adaptation scheme in multicarrier (MC) direct-sequence code-division multiple-access (DS/CDMA) communications under the assumption that channel state information is provided at both the transmitter and the receiver. We consider, as a power allocation strategy in the frequency domain, transmitting each user's DS waveforms over the user's sub-band with the largest channel gain, rather than transmitting identical DS waveforms over all sub-bands. We then consider rate adaptation in the time domain, where the data rate is adapted such that a desired transmission quality is maintained.We analyze the BER performance of the proposed joint power and rate adaptation scheme with fixed average transmission power, and compare the performance to that of power and rate adapted single carrier DS/CDMA systems with RAKE receiver.

We propose an efficient frequency-time domain resource allocation scheme in multicarrier (MC) direct-sequence code-division multiple-access (DS/CDMA) communications. We consider, as a power allocation strategy in the frequency domain, transmitting each user’s DS waveforms over the user’s sub-band with the largest channel gain. We then consider rate adaptation in the time domain, where the data rate is adapted such that a desired transmission quality is maintained. We analyze the achievable average data rate of the proposed scheme with fixed average transmission power, and compare the performance to single carrier DS/CDMA systems with power and rate adaptations.

We propose a combined power and rate adaptation scheme in direct-sequence code division multiple access (DS/CDMA) communications over Nakagami fading channels. The transmission power proportional to Gi p is allocated to the data transmission of user i, where Gi is the channel gain for user i, and p is a real number, and the data rate (i.e. spreading gain) is jointly adapted so that a desired transmission quality is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme has considerable performance improvements over power only adaptation and rate only adaptation for a range of system parameters.