A family of binary sequences is presented and proved to have optimal correlations and large linear span. It includes the small set of Kasami sequences, No sequence set and TN sequence set as special cases. A lower bound on the linear span of the family is provided. With suitable choices of parameters, it is proved that the family has exponentially larger linear spans than both No sequences and TN sequences.

A family of [2n- 1, 5n/2, 2n-1- 2n/2] codes with n even is proposed and the weight distribution is completely determined. These codes are applied to construct new families of binary sequences with period (2n$1), including the small set of Kasami sequences. The binary sequence families have the same family size and correlation values as the large set of Kasami sequences

This paper studies the performance of ultra-wideband (UWB) radio communications systems employing phase shift keying (PSK) modulation and fully saturated power amplifiers through additive white Gaussian noise (AWGN) channel or Rayleigh fading channel. An impulse response method is provided to analyze the signal-to-noise ratio (SNR) degradation. Both convolutional code and turbo code are employed with the Viterbi decoding and the iterative decoding, respectively. The decoding algorithms are modified for the Rayleigh fading channel. Near optimal bit error rate (BER) performance is achieved when employing either convolutional code or turbo code. The simulation results match the derivation. Therefore, fully saturated power amplifiers can be employed in UWB PSK systems to significantly reduce radio cost, simplify radio circuit, and increase battery life for portable terminals.

This paper compares the performance of on-off keying (OOK) modulation and subcarrier phase shift keying (PSK) modulation through an optical wireless channel. The bit error rate (BER) for a turbulent channel is derived for optical wireless communication systems employing OOK or subcarrier BPSK. A lower bound is derived for BER performance when fixed-threshold OOK is used. It is also shown that the BER performance of the optical wireless communication system, employing subcarrier PSK modulation, is more than 3 dB better than that of a compatible system employing fixed-threshold OOK modulation at BER=10/sup -6/ and with turbulence parameter /spl sigma/=0.1. When /spl sigma/ is 0.2 and fixed-threshold OOK is employed, the BER performance never falls down to 10/sup -4/. The BER performance degradation of optical wireless communication systems employing subcarrier BPSK between /spl sigma/=0.1 and /spl sigma/=0.2 is only 2.5 dB at BER=10/sup -6/.

The paper studies the performance of phase modulation through a fully saturated power amplifier and AWGN channel for broadband wireless systems. A nonlinear model for the fully saturated power amplifier is derived. The equivalent impulse response method is provided to analyze the SNR degradation. Both convolutional code and turbo code are used. Viterbi decoding and iterative decoding are employed, respectively. Near optimal BER performance is achieved employing either convolutional code or turbo code. The simulation results match the derivation. Therefore, it is practical to employ phase modulation and fully saturated power amplifiers in broadband wireless/satellite networks and sensor networks for ideal battery life, low cost and high terminal reliability.

This paper proposes a multiple access algorithm for broadband satellite communication networks. The access channel is the slotted Aloha contention channel. The performance of the algorithm is analyzed considering user terminal time uncertainty, power uncertainty, minimizing co-channel interference as well as non-perfect feedback information from the central receiver. It is shown that reliable access can be achieved with a reasonably small delay by employing the proposed algorithm.

A frequency synchronization method is proposed and analyzed for global satellite communications systems employing low Earth orbit satellites or medium Earth orbit satellites. In these systems, the Doppler shift varies randomly and can be more than ten times larger than the symbol rate. The proposed method uses the satellite as the reference point and corrects frequency errors accordingly. It is shown the proposed method can achieve negligibly small frequency errors. By employing this method, the system bandwidth can be fully utilized and guard bands are no longer needed.

This paper proposes an algorithm for user terminals in broadband slotted Aloha networks to jointly succeed in time synchronization, power adjustment, and registration to the network control center. The performance is analyzed considering nonnegligible initial time uncertainty, nonnegligible power uncertainty, and minimizing cochannel interference as well as binary feedback from the central receiver. User terminal initial power setting can be performed using the method developed in this paper to make sure the interference generated in the registration stage is negligible. The algorithm is sufficient to keep the false registration probability less than any number required by the network. It can help broadband slotted Aloha networks to significantly reduce system cost through employing a large number of inexpensive user terminals with non-negligible time uncertainty and nonnegligible power uncertainty.

Throughput bounds are attained for random channel access multichannel code-division multiple-access (CDMA) systems and spread slotted Aloha systems employing multiuser receivers. It is shown that the normalized throughput of these two systems reaches 1.0 exponentially fast in the region r/K0. The maximum throughput of the random channel access multichannel CDMA systems is found as K-/spl radic/(1-(1/M))KlogK-O(logK), where M is the number of channels in the system. The maximum throughput is reached when the average number of simultaneous users is r/sub m/=K-/spl radic/((1-(1/M))KlogK))+O(/spl radic/(K/logK)). The maximum throughput of the spread slotted Aloha systems is K-/spl radic/(KlogK)-O(log K). The maximum throughput is reached when the packet arrival of Poisson distribution has the arrival rate /spl lambda//sub m/=K-/spl radic/(KlogK)+O(/spl radic/(K/logK)).

A novel method of frequency synchronization is proposed for global mobile satellite communications systems. It is shown that this method is optimal to handle dynamic frequency errors of large range dominated by Doppler. Frequency synchronization is also studied for diversity calls and systems with large delays.

A statistical characterization of the complexity function of the Verdu optimum multiuser detection (VOMD) algorithm is presented for a communication system employing a finite number of randomly accessed orthogonal channels and a finite number of simultaneous users. Multichannel code-division multiple-access (CDMA) systems are proposed. It is proved that the probability, in which the individual channel complexity is greater than A/sup r(1+/spl alpha/)/, approaches zero exponentially fast as the average number of simultaneous users in each channel increases, where A is the modulation alphabet size and /spl alpha/>0. When the number of simultaneous users is large, the complexity of applying the VOMD algorithm to each individual channel is negligible when compared with the complexity of applying the same algorithm directly to the traditional single-channel CDMA system supporting the same number of simultaneous users. The probability distribution of the joint complexity function of the aggregate system is found. It is shown that when the number of simultaneous users is large, the joint complexity function is negligible compared with applying the VOMD algorithm directly to the traditional single-channel CDMA system supporting the same number of simultaneous users. Therefore, a multichannel CDMA communication system can support a comparable population of simultaneous users to the traditional single-channel CDMA system of comparable bandwidth, while reducing the complexity of optimum multiuser detection to a practical level.