An even harmonic quadrature mixer (EH-QMIX) with a balanced configuration is proposed for a direct conversion receiver. The unit even harmonic mixer (EHMIX) used for I/Q paths consists of two anti parallel diode pairs (APDPs) and a pair of diplexers. When the second harmonic of LO (2LO) from the LO section is applied to the LO port as a spurious component, a conventional single-ended EHMIX using APDP converts the 2LO leakage from the LO section into the baseband and the d.c. offset and the self-detected LO noise arise at the baseband degrade the sensitivity. This proposed balanced EHMIX configuration can cancel out the 2LO leakage in itself. Therefore, the d.c. offset and the LO noise are significantly suppressed and the degradation of the sensitivity can be avoided. The suppression characteristic of the d.c. offset and the LO noise are verified by the simulation and the measurements. By using this balanced configuration, the fabricated EH-QMIX achieves wider frequency band characteristic than that of the single-ended EH-QMIX, and it shows 20% relative bandwidth at L-band.

This letter presents an efficient multichannel low-IF reception scheme that improves digital communication quality in the sense of BER performance. Created by simply adding cosine rolloff filters to the conventional multichannel receiver, the proposed receiver achieves much higher accuracy than the conventional one.

In this paper an adjacent channel interference (ACI) cancellation scheme with undersampling for multi-channel reception is proposed and investigated. Low-IF receiver architecture is used in the multi-channel reception scheme. In this system, signal in the adjacent channel causes interference to the desired signal. The ACI cancellation scheme with analog filter bank has been proposed to mitigate the influence from the adjacent channel [10]. Undersampling technique is applied in this system in order to lower the required sampling frequency and power consumption. The effects of the adjacent channel to the undersampling technique in this scheme is examined and discussed.

This letter proposes a compensation method that can alleviate the problem of I/Q mismatch generated in the direct-conversion receiver of OFDM systems. In the proposed method, the amount of I/Q mismatch is estimated using null-carriers in transmitted signals, and it is subtracted from received symbols to suppress I/Q mismatch effects. Simulations show experiments that the proposed method can effectively eliminate the I/Q mismatch effects.

In this paper, we present laboratory and field experimental results using High Speed Downlink Packet Access (HSDPA) test-beds in order to reveal the actual HSDPA performance based on key technologies such as base station (BS) scheduling, adaptive modulation and coding, hybrid automatic repeat request, and advanced receiver design. First, this paper evaluates the effects of advanced user equipment capabilities such as the maximum number of multi-codes, transmit diversity, receive diversity, and a chip equalizer. Increases in throughput of 60% and 85% due to using 10 and 15 codes were observed compared to 5 codes, respectively. The gain of 22% was obtained by applying closed-loop transmit diversity to the HSDPA network. Receive diversity improves the throughput in the region from low to high signal-to-interference ratio, and the gain of 45% was obtained by applying receive diversity to the conventional RAKE receiver. A throughput gain of approximately 17% due to the use of the chip equalizer was obtained and it was observed mainly in the high Ior/Ioc region and under multi-path conditions. Second, field experiments are conducted to elucidate the effects of multi-user diversity using a BS scheduling algorithm, and reveal that proportional fairness scheduling provides both the increase in sector throughput of 18% and a sufficient degree of fairness among users. The transmit control protocol (TCP)-level throughput performance is also investigated in order to reveal the actual end-user throughput. The results show that the throughput rate of approximately 90% of the throughput of the MAC-hs layer is achieved in the TCP layer in the laboratory experiments and in the field experiments.

Broadcast encryption technology enables a sender to send information securely to a group of receivers excluding specified receivers over a broadcast channel. In this paper, we propose a new key-tree structure based on Rabin cryptosystem, and an access control scheme using the structure. We show the security of the access control scheme and construct a new broadcast encryption scheme based on it. The proposed broadcast encryption scheme is a modification of the complete subtree method and it reduces the number of keys a receiver stores to one. There have been proposed some modifications of the complete subtree method which minimize the number of keys for a receiver to one, and the most efficient one among them with respect to the computational overhead at receivers is based on RSA cryptosystem. The computational overhead at receivers in our scheme is around log2e times smaller than the most efficient previously proposed one, where e is a public exponent of RSA, and the proposed scheme is the most efficient among tree based one-key schemes. This property is examined by experimental results. Our scheme achieves this reduction in the computational overhead in exchange for an increase in the size of nonsecret memory by [log n * few (e.g. eight)] bits, where n is the total number of receivers.

In this letter, we evaluate the M-BOK based DS-UWB system that uses a space-time block code (STBC) with Rake receivers in the WPAN environment. The conventional DS-UWB system doesn't ensure receiver reliability for the WPAN envrionment due to multipath fading, while the proposed M-BOK based DS-UWB system employing a STBC can overcome multipath fading causing attenuation of receiver reliability in the WPAN environment. In addition, a simple diversity combining receiver, called PRake receiver, shows the performance similar to that of a ARake receiver using the ideal diversity combining and reduces the receiver complexity.

Software-Defined Radio (SDR) represents a major paradigm shift in the design of radios, allowing a large fraction of the functionality to be implemented through programmable signal processing devices, enabling the radio to change its operating parameters to accommodate new air interface, features and capabilities. However, the actual realization of innovative and software-reconfigurable receiver diversity at mobile handsets in intermediate frequency band to provide wide-ranging benefits, including more effective filtered result, less cost of the mixed channel access, improved capacity, better link reliability, and reduced power consumption, has been slowed down largely due to an absence of effective architecture reducing the complexity of adaptive combining algorithms. This paper proposes a novel reconfigurable architecture for adaptive space diversity at handsets in MC-CDMA (multicode code-division multiple-access) systems. The key to which is the development of a valid and effective alternative to the time-consuming multiplication operation and despreading acquisition. A software definable algorithm can become a multiplier-free architecture if it can restrict the weight factors to power-of-two values and repetitive gradient search procedure to contain shift operations and predicate functions. The results of numerical simulation and experimentation confirm the expectation that the constrained approach should perform comparably to, but not better than the traditional diversity algorithm. That is, the feasibility of SDR depends on its trading some performance for reduced computational complexity, improved area efficiency and less power consumption.

This paper presents an even harmonic quadrature mixer (EH-QMIX) with a simple filter configuration and an integrated LTCC module including LNAs, band rejection filters (BRFs), and the proposed EH-QMIX for W-CDMA direct conversion receiver (DCR). Since the DCR has no spurious responses, a BRF instead of a high-Q band pass filter can be applicable for eliminating undesired signals and it can be built in the LTCC substrates easily. As LO frequency is half of RF frequency in the EH-QMIX, diplexer can be composed of simple filters and it can be also integrated in the substrates. As a result, the whole RF circuits of the EH-DCR using a proposed EH-QMIX are integrated in the LTCC module and miniaturization of the receiver is achieved. Moreover, in order to suppress the degradation of the amplitude and the phase imbalances in the quadrature mixer caused by interferences of signals, RF characteristics of the circuits in the mixer such as reflection coefficients, isolations are discussed. A developed LTCC module shows good performances for W-CDMA direct conversion receiver.

In this paper, we propose an ICI mitigation method for MIMO OFDM using turbo detection technique. In order to reduce the computational complexity, we present a method for dividing the received frequency-domain signals into subbands and the manner of division varies with each iteration, joint soft ICI cancellation and decoding is then performed on each subband. To perform iterative ICI mitigation, the estimation of the time-variant channel using a great quantity of pilot tones is needed, which results in poor spectral efficiency. We then propose a method to reduce the required scatter pilot tones, which is differentially-modulated-pilot scheme. Moreover, the estimation can be constructed based on EM-type algorithms to further reduce the computational complexity. Finally, the results of computer simulations demonstrate that the proposal can provide significant performance improvement.

The performance of a feedback-type adaptive array antenna (AAA) system placed only at a base station (BS) in an FDD/DS-CDMA system remains insufficiently clear. We evaluate the performance of this system by considering the effect of a rake receiver, spacing distance between antennas, the maximum Doppler frequency (fd), and control delay time (Td) on BER performance. In this system, the mobile station (MS) determines optimum weights of antenna elements and sends them back to BS as feedback information. We assume that the optimum weights are not quantized. Thereby, we estimate the performance degradation of 3GPP transmit diversity system, where the feedback information is quantized using a few bits. Computer simulation results show that the rake receiver achieves better BER performance because of the time diversity effect with rake receiver. The AAA with a wide antenna spacing gives high diversity gain for the received signals. For a high value of fd Td, BER performance becomes worse because weighting factors cannot follow the changing speed of channel characteristics. The degradation in performance of a 3GPP system is clarified.

A polynomial expansion linear detector (PELD) based turbo receiver is proposed for single-carrier zero-padding block transmission (ZP-SCBT) systems over the single-input single-output (SISO) and multiple-input multiple-output (MIMO) frequency selective channels. The performance is compared with the minimum mean square error (MMSE) and match filter (MF) based turbo receivers. It is shown that the PELD-based turbo receiver provides a good trade-off between performance and complexity compared with the other two alternatives.

Error performance of DS-CDMA is discussed over independent Rayleigh faded multipath channel employing selective Rake (SRake) receiver. Simple-to-evaluate and accurate error probabilities are given following Holtzman's simplified improved Gaussian approximation (SIGA). Comparing with SIGA, the validity of standard Gaussian approximation (SGA) is then verified. It is shown that SGA is accurate for SRake until some number of combined paths beyond which it becomes optimistic. It is also shown that as compared to single user performance, the SRake performance is relatively less degraded by multiple access interference (MAI) while the number of combined paths is small.

In this paper, we propose a single-user strategy for demodulating asynchronous direct-sequence code-division multiple access (DS/CDMA) signals for improving the performance of the adaptive receiver in fast fading channels. Since the adaptive receiver depends on the channel coefficient of all users, it cannot be implemented adaptively in fading channels due to severe tracking problem. A proposed adaptive receiver based on the modified minimum mean-squared-error (MMSE) criterion is used for solving this problem. By simulation, it is verified that our proposal is a promising method to solve the problem, and the results show that the proposed adaptive receiver has substantially larger capacity than the conventional adaptive receiver in fast fading channels.

In this paper we present a novel method for improving RAKE receiver reception in UWB systems. Due to the fact that practical pulses that can be produced for UWB-IR (Ultra Wideband-Impulse Radio) may occupy a longer time than the typical multipath resolution of the actual UWB channel, multiple channel components may arrive within this typical pulse width. Performance degradation may occur due to the resulting intrapulse (overlapping received pulses) interference. We here propose an adaptive, pilot aided RAKE receiver for UWB communications in the multipath environment. The proposed system estimates the actual received signal with intrapulse interference in each RAKE finger using projections onto a Hadamard-Hermite subspace. By exploiting the orthogonality of this subspace it is possible to decompose the received signal so as to better match the template waveform and reduce the effects of intrapulse interference. By using the projections onto this subspace, the dimension of the received signal is effectively increased allowing for adaptive correlator template outputs. RAKE receivers based on this proposal are designed which show significant performance improvement and require less fingers to achieve required performance than their conventional counterparts.

The basic carrier sense multi-access control scheme for multicast communications in wireless ad hoc networks suffers from the well know hidden terminal problem. The data packet collision probability is relatively high, and the packet delivery ratio is sensitive to the network topology, nodes distribution and traffic load. In this paper, we generalize the virtual carrier sense collision avoidance approach to reduce packet collisions in multicast communications. The sender and receivers exchange RTS and CTS packets to reserve the channel. When more than one receivers reply with CTS packets, the sender will detect an "expected" collision which may be interpreted as a valid "clear-to-send" signal provided the collision satisfies the given timing requirements. Together with a receiver-initiated local recovery mechanism, the reliability and packet delivery ratio can be improved to close to 100%.

In this letter, we propose a 2-D receiver structure for multicarrier code division multiple access (MC-CDMA) systems with the reduced-rank multistage Wiener filter. Due to the fast convergence property of the reduced-rank processing, it outperforms MMSE-based receivers with the classical Wiener solution, which is estimated by using a limited number of samples.

A dual-mode, triple-band RF front-end receiver for GSM900, DCS1800 and WCDMA is presented in this paper. This chip uses low-IF and zero-IF receiver architectures for GSM and WCDMA respectively to fulfill the entirely different system requirements of the two standards. It consists of three parallel LNAs and down-conversion mixers with on-chip LO I/Q generations. The receiver front-end is implemented in a standard 0.25 µm CMOS process and consumes about 30-mA from a 2.7-V power supply for all modes. The measured double-side band noise figure and voltage gain are 3 dB, 36 dB for the GSM900, 5.9 dB, 31 dB for the DCS1800, and 4.3 dB, 29.6 dB for the WCDMA, respectively.

In this paper a new adjacent channel interference (ACI) cancellation scheme for multi-channel signal reception with low-IF receivers is investigated through the experiment. In the low-IF receivers, the signal in the mirror frequency causes interference to the desired signal. In the proposed analog-digital signal processing scheme, channel selection is made by analog complex band pass filter and the signal is reconstruct by Wiener filter to eliminate the interference effect in order to improve the performance.

A RF front-end chip for a dual-band Global Positioning System (GPS) receiver for L1 and L2 bands is designed using 0.25 µm CMOS technology. All function blocks of the GPS front-end are integrated onto one chip. The low noise amplifier has input matching over a wide frequency range to handle the L1 and L2 bands. This receiver uses a dual-band image-reject mixer with the quadrature mixer sharing a transconductor stage. This configuration enables the RF blocks to be shared with the L1 and L2 bands. The receiver has a chip area of 3.16 mm3.16 mm, and consumes 35 mA at 2.5 V.