The present paper introduces a novel construction of structured ternary sequences having a zero-correlation zone (ZCZ) for both periodic and aperiodic correlation functions. The cross-correlation function and the side lobe of the autocorrelation function of the proposed sequence set are zero for phase shifts within the ZCZ. The proposed ZCZ sequence set can be generated from an arbitrary Hadamard matrix of order ℓh. For m > 0, the sequence set of order (m+1) is constructed from the sequence set of order m by sequence concatenation and interleaving. The sequence set of order m has 2 × 4msubsets of size ℓh. The length of the sequence is equal to 4 (8m(ℓh+1)+2m(4m-1) /3). The phase shift of the ZCZ for the entire sequence set is from -(2m-1) to (2m-1). The sequence set of order 0 is coincident with the rows of the given Hadamard sequence with no ZCZ. The subsets can be associated with a perfect quadtree of height m with 4mleaves. The r-th sequence subset is associated with the r-th leaf. For a longer distance between the corresponding leaves to the r-th and s-th sequences, the ZCZ of the r-th and s-th sequences is wider. This tree-structured width of ZCZ of a pair of the proposed sequences enables flexible design in applications of the proposed sequence set. The proposed sequence is suitable for a heterogeneous wireless network, which is a candidate for the fifth generation of radio access networks.

In recent, to achieve several services with the information product, high speed and high quality systems of wireless communications are demanded. To achieve this demand, orthogonal frequency division multiple access (OFDMA) has been proposed. In a wireless network, the transmitted signal of each user has independent channel fluctuation characteristics. By using this characteristic, the multiuser diversity (MUDiv) effect can be obtained, and MUDiv/OFDMA has been proposed. Before now, we have proposed a low complexity MUDiv/OFDMA. However, it degrades the system performance compared with the conventional MUDiv/OFDMA in the channel as a Pyramid model. To solve this problem, in this paper, we propose the method to mitigate the deep faded channel for a low complexity MUDiv/OFDMA with the relay node allocation.

For mobile systems higher than 3G, multi-rate data service is becoming an important issue. This paper proposes a multi-rate block-spreading CDMA system as an efficient scheme which is capable of intra-cell-interference free operation and inter-cell-interference reduction by a factor of reciprocal of the spreading factor. With a use of an accurate pilot transmission scheme, it is shown that a high frequency utilization efficiency can be achieved for various mixed data rate services.

We have proposed a method for increasing the information transmission rate and the frequency usage rate based on a new method for estimating multipath channels and spread time signals convolution. We used a pilot signal and data-transmission signals in the same frequency and in the same time. For this purpose, we used the complete complementary code on approximately synchronized systems. The information transmission rate came to (1.3/k) chip/bit, where k was the QAM factor. In this paper, a new usage method for a complementary code is proposed. The new method is far simpler than the old method. By applying the proposed usage method for a complete complementary code on the above high rate information transmission method, the high rate information transmission can be realized easier.

A new signal demodulation system for CDMA receivers is proposed. This system has an effective function of canceling the interference noise components in the received symbol frames. For a target symbol frame to be detected, the differential frames are produced, each of which is made by subtracting one of the neighboring symbol frames from the target frame. The interference noise being left in some of the differential frames is much less than that in the target frame. By demodulating only such noise cancelled differential frames that have been estimated with effective analyzing sequences, the information conveyed on the target frame with a heavy interference can be detected. The simulation indicates powerful canceling performance for all the possible interference disturbance is achieved.

This correspondence tries to construct a direct-sequence spread-spectrum multiple-access communication system, so that the difficulty of wiretapping from insiders' and outsiders' attacks increases and the worst case error probability decreases, as much as possible. Bent sequences with optimal periodic correlation properties are assigned to users, as spreading sequences corresponding to secret keys.

Suehiro (1985) has proposed a quadriphase signal design method for the uplink of the cellular CDMA mobile communication systems. The designed signals work without co-channel interference when the systems are synchronized approximately. The designed signals are free from the influence of multipath signals within some delay. The filters for the designed signals can be realized as SAW devices. We assign plural quadriphase signals as M-ary signals for each user so that the information-transmission rate is increased. The property of without co-channel interference remains the same, but the multipath property becomes a little bit worse. The filters for M-ary signals can also be realized as SAW devices.

Hadamard matrices are often used for some applications, such as error-correcting codes and spread sequences. This article gives the construction of complex Hadamard matrices of order p/sup n/, where p is prime and n is even. The complex Hadamard matrices include bi-phase Hadamard matrices whose elements take {-1, +1}, and four-phase Hadamard matrices whose elements take {/spl plusmn/1, /spl plusmn/j} with j=/spl radic/(-1).

The real-valued bent function was previously introduced by the authors (1991) as a generalization of the usual p-ary bent function, p a prime, in such a way that the range of the function is the set of real numbers, i.e. not restricted to GF(p). The real-valued bent function was used to construct a family of 2/sup n/2/ balanced quadriphase sequences of period 2/sup n/-1 with optimal periodic correlation properties, where n is a multiple of four. A class of real-valued bent functions that map the set of all the m-tuples over GF(2) into the set (0,1/2,1,3/2) for an arbitrary m is given. This is applied to generalize a previous construction to the case where n is even, i.e. not restricted to a multiple of four. It is also shown that the quadriphase sequences given by T. Novosad can be considered as one kind of sequence constructed by real-valued bent functions. Conditions are given for some families of the quadriphase sequences constructed by some real-valued bent functions to be balanced. The exact distributions of the periodic correlation values are derived for the families of the balanced quadriphase sequences.>