Inter-domain communications on a chip require a synchronizer to resolve the timing problems between an input and a clock of a destination. This paper presents a parallel flop synchronizer and its interface circuit for transferring asynchronous data to the clock domain. The proposed scheme uses a bank of independent two-flops in parallel and supports a two-phase handshake protocol. Compared to the conventional two-flop synchronizer, performance analysis shows that the proposed scheme can reduce latency up to one and a half of clock cycles while retaining its safety to a tolerable level. All designs have been implemented in a 0.25 µm CMOS technology to verify performance analysis of the proposed synchronization.

A hybrid CDMA/TDMA, a combination of CDMA and TDMA, is proposed as a MAC protocol for wireless ATM networks. TDMA offers the ability to integrate different types of services in a flexible way by the use of multiple slots per frame, while CDMA allows multiple users to transmit simultaneously using their own codes. To reduce the multiple access interference in each slot, the channel access is controlled by an access permission probability or a round robin method. A shared code scheme is adopted to utilize the given code resource efficiently. The results of simulation show that the proposed scheme gives better performance than the JCP algorithm.

This paper proposes a novel MAC scheme over APON based on the cell arrival timing information to provide residential and small business customers with multimedia services. The proposed scheme supports the frame format of ITU-T recommendation G.983 and also provides diverse ATM service classes such as CBR, rtVBR, nrtVBR, ABR, and UBR traffics. Each service is allocated on the basis of priority and cell arrival timing information. Especially, the CBR and rtVBR services, which are sensitive to delay and CDV, are allocated with higher priority and more exact arrival timing resolution which is achieved with specific coding and ranging procedure. For the proposed MAC scheme, we present grant field format, minislot format, and bandwidth allocation algorithm. Computer simulation results show that the performance of the proposed scheme is significantly improved in terms of CDV and delay time in case of CBR and rtVBR services, comparing with the normal FIFO scheme.

Adaptive interference suppression strategies based on the transform domain approach are proposed for a satellite on-board filter bank under tone-type interferences. In the proposed methods, the three kinds of algorithms to compute the threshold level are jointly employed with the notch filter or the clipper. Simulation results show that the proposed schemes significantly improve performance under interfering environments, compared to the no suppression case.

In this paper, we propose a new fair queueing algorithm to improve cell delay variation (CDV) for real-time service categories and to make efficient use of system resources for multimedia traffic in high speed ATM networks. The proposed algorithm is called the delay variation-based fair queueing (DVFQ) algorithm, which is based on per-VC queueing to improve CDV and fairness for each VC of real-time services such as CBR and rt-VBR. In DVFQ algorithm, we define two fairness indexes, which indicate the degree of the fairness of CDV at the rate of each VC, and the degree of impartially sharing the bandwidth between the scheduled cells for each VC. The simulation results for both heavily and lightly loaded conditions show that DVFQ algorithm provides better performances in terms of the CDV, the CDV fairness, and the service fairness than those of FCFS for real-time service.

In this paper, we investigate two packet scheduling schemes over the downlink of DS/CDMA systems to support packet data service. These schemes are the code division multiplexing (CDX)-based packet scheduling and the time division multiplexing (TDX)-based packet scheduling. To evaluate each scheme more effectively, we derive the throughput gain of the downlink as a performance measure based on the power constraint equation. In addition, the packet transmission delay of each scheme is derived and compared each other when the packet lengths of the concurrent data users are independently and identically distributed according to the exponential distribution. As the downlink capacity is quite related to the orthogonality factor, our analysis shows from the results that the throughput gain and the transmission delay are highly dependent on this factor. Furthermore, it is shown that the TDX scheduling scheme in CDMA downlink affords better performances than the CDX scheduling scheme, except when the orthogonality factor is around 1.

A mutated adder architecture utilizing a mixture of carry propagation schemes is proposed to design a delay-area efficient adder which were not available in an ordinary design space. Further, we develop an optimization method based on integer linear programming to search the expanded design space of the mutated adder.

The Erlang capacity of multi-service multi-access systems supporting several different radio access technologies was analyzed and compared according to two different operation methods: the separate and common operation methods, by simultaneously considering the link capacity limit per sector as well as channel element (CE) limit in a base station (BS). In a numerical example with GSM-like and WCDMA-like sub-systems, it is shown that we can get up to 60% Erlang capacity improvement through the common operation method using a near optimum so-called service-based user assignment scheme when there is no CE limit in BS. Even with the worst-case assignment scheme, we can still get about 15% capacity improvement over the separate operation method. However, a limited number of CEs in BS reduces the capacity gains of multi-service multi-access systems in both the common operation and separate operation. In order to fully extract the Erlang capacity of multi-service multi-access systems, an efficient method is needed in order to select a proper number of CE in BS while minimizing the equipment cost.

Multimedia Wavelength Division Multiple Access (M-WDMA) specially designed to accommodate multimedia traffic is a well-known media access control (MAC) protocol. This paper extensively analyzes the throughput of M-WDMA. Specifically, this analysis considers a wide range of network conditions including varying traffic loads, probabilistic occupancy of time segment, various traffic distribution patterns (TDPs) and channel sharing methods (CSMs) under both symmetric and asymmetric traffic load patterns (TLPs). Thus, the analytic behavior of M-WDMA can be investigated for designing a WDMA network managing multimedia traffic under practical environments.

This paper describes a CORDIC-based direct digital frequency synthesizer in comparison with a ROM-based architecture. To optimize the hardware design parameters, we perform numerical analysis of the quantization effects for ROM and CORDIC-based architectures. The hardware costs of them are estimated in FPGA, which shows that the CORDIC-based architecture becomes better than the ROM-based when the required accuracy is 9 bits or more.

In this paper, we propose a Call Admission Control (CAC) scheme for the Direct Sequence-Code Division Multiple Access (DS-CDMA) systems supporting voice and data services and analyze the Erlang capacity under the proposed CAC scheme. Service groups are classified by Quality of Service (QoS) requirements such as the required Bit Error Rate (BER) and information bit rate, and Grade of Service (GoS) requirement such as required call blocking probability. Different traffics require different system resources based on their QoS requirements. In the proposed CAC scheme, some system resources are reserved exclusively for handoff calls to have high priority over new calls. Additionally, the queueing is allowed for both new and handoff data traffics that are not sensitive to delay. As a performance measure of the suggested CAC scheme, Erlang capacity is introduced. For the performance analysis, a four-dimensional Markov chain model is developed. As a numerical example, Erlang capacity of an IS-95B type system is depicted, and optimum values of system parameters such as the number of reservation channels and queue lengths are found. Finally, it is observed that Erlang capacity is improved more than 2 times by properly selecting the system parameters with the proposed CAC scheme. Also, the effect of handoff parameters on the Erlang capacity is observed.

In this paper, we propose an analytical procedure for the Erlang capacity in the reverse link of the DS-CDMA systems supporting voice and data services with the limited number of channel elements. Especially, we focus on IS-95B type systems with sectorized directional antenna that support the medium data rates for data traffic by aggregating multiple codes in both directions, to and from the mobile device. For the performance analysis, a 6-dimensional Markov chain model is developed, and the Erlang capacity is depicted as a function of the offered traffic loads of voice and data. The call blocking is caused not only by the scarcity of channel elements that perform the baseband spread spectrum signal processing for the given channel in the base station, but also by insufficient available channels per sector. The effect of the different Grade of Service (GoS) requirements on the Erlang capacity is observed, and the optimum values of the system parameters such as channel elements are selected with respect to the Erlang capacity. Furthermore, we expand our approach to the multi-FA systems that support multiple CDMA carriers more than one. It is observed that Erlang capacity for a high FA can be well estimated through the linear regression with the Erlang capacity results of low FAs.

The performance of asynchronous fast frequency hopping-multiple access (AFFH-MA) systems with multiple hops per bit is investigated with a linear-combining receiver in Rayleigh fading. We present an accurate approximation method for evaluating the error probability by using the characteristic function, Taylor series, and Gauss-Chebyshev quadrature rule. We will show that the proposed method provides an accurate approximation, compared with a simple Gaussian approximation. The validity of proposed analytic works is verified through Monte Carlo simulations.

This paper proposes the Multimedia Pre-allocation WDMA (MP-WDMA) media access control (MAC) protocol to provide an efficient packet transfer service for metro-wavelength division multiple access (WDMA) networks. MP-WDMA considers three traffic types: constant bit rate (CBR), variable bit rate 1 (VBR1), and VBR2 traffic for a multimedia service as categorized in Multimedia WDMA (M-WDMA) MAC protocol. MP-WDMA is based on pre-allocation WDMA (P-WDMA), but the three traffic types are simultaneously allocated at one time slot, and one of them is selected through low bandwidth control signaling. Namely, a station assigns appropriate priority to input traffic, based on proposed traffic priority rules in MP-WDMA in order to determine the type of traffic. Accordingly, MP-WDMA can reduce station complexity as well as the possibility of idle time slot occurrences, compared with M-WDMA. Additionally, we analytically investigate the channel utilization and channel access delay of MP-WDMA and compare them with those of M-WDMA to find a proper MAC protocol for the networks. As a result, MP-WDMA supports maximally 30% higher channel utilization than M-WDMA regardless of channel and traffic conditions. Furthermore, MP-WDMA reduces the channel access delay of the delay-sensitive VBR2 traffic at the cost of increasing the channel access delay of the delay-insensitive VBR1 traffic. In this regard, MP-WDMA is suitable for the networks in terms of station complexity, channel utilization, and the channel access delay for VBR2 traffic.

The bit error rate (BER) degradations of fast frequency hopping multiple access (FFH-MA) systems due to the frequency and timing offsets are investigated over a Rician fading channel. It is shown that as the received average SNR increases, the BER is affected much larger by frequency and timing offsets. When the frequency offset or the timing offset exists alone, the BER of the FFH-MA system is degraded much more due to the timing offset than due to the frequency offset. The BER degradation due to both the frequency offset and the timing offset is larger than the sum of the degradations due to each offset.

In this letter, a resource allocation scheme is proposed to efficiently utilize the resource of CDMA systems with respect to the throughput. When we let the throughput be a function of various data rates for multimedia traffics, the scheme is to find the optimum set of data rates for concurrent user groups with which we can achieve the maximum throughput. It is also shown that the optimum data rate set always includes one non-trivial rate while all the others keep the minimum required data rate.

A new load balanced channel sharing method (CSM), namely Heuristic Traffic Load Balanced (HTLB) CSM, is proposed for metro-wavelength division multiple access (WDMA) networks. In particular, HTLB CSM is designed to be effective for pre-allocation based medium access control (MAC) protocols by balancing traffic loads corresponding to pre-assigned destinations per time slot. As a result, HTLB CSM is shown to provide lower time complexity than the well-known sub-optimal load balanced CSM, MULTIFIT CSM. Furthermore, the Jain Index of the HTLB CSM is shown to be higher and more consistent than the MULTIFIT CSM and other pre-fixed CSMs under diverse traffic conditions.

As an alternative solution to provide the quality of services (QoS) for broadband access over Ethernet Passive Optical Network (EPON), we present the usage of MAC control message for plural class queues and a traffic-class burst-polling based delta dynamic bandwidth allocation (DBA), referred to as TCBP-DDBA, scheme. For better QoS support, the TCBP-DDBA minimizes packet delays and delay variations for expedited forwarding packet and maximizes throughput for assured forwarding and best effort packets. The network resources are efficiently utilized and adaptively allocated to the three traffic classes for the given unbalanced traffic conditions by guaranteeing the requested QoS. Simulation results using OPNET show that the TCBP-DDBA scheme performs well in comparison to the conventional unit-based allocation scheme over the measurement parameters such as: packet delay, packet delay variation, and channel utilization.

We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in Eb/N0 comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10-5.

To sample a band-limited analog signal directly from the high frequency down to the baseband for the digital signal processing with significantly reduced computation, several concepts of the bandpass sampling are introduced. In this paper, a robust bandpass sampling scheme when there exist frequency deviations due to the channel effect and hardware instability is proposed for practical use, and the effects of the frequency deviations are discussed to select a proper sampling frequency.