This paper presents a novel spectrum sensing technique based on selection diversity combining in cognitive radio networks. In general, a selection diversity combining scheme requires a period to select an optimal element, and spectrum sensing requires a period to detect a target signal. We consider that both these periods are required for the spectrum sensing based on selection diversity combining. However, conventional techniques do not consider both the periods. Furthermore, spending a large amount of time in selection and signal detection increases their accuracy. Because the required period for spectrum sensing based on selection diversity combining is the summation of both the periods, their lengths should be considered while developing selection diversity combining based spectrum sensing for a constant period. In reference to this, we discuss the spectrum sensing technique based on selection diversity combining. Numerical examples are shown to validate the effectiveness of the presented design techniques.

Increasing demand in data-traffic has been addressed over the last few years. It is expected that the data-traffic will present the significant part of the total backbone traffic. Accordingly, much more transmission systems will be required to support this growth. A free space optic (FSO) communication is the greatest promising technology supporting high-speed and high-capacity transport networks. It can support multi Gbit/s for few kilometers transmission distance. The benefits of an FSO system are widespread, low cost, flexibility, immunity to electromagnetic field, fast deployment, security, etc. However, it suffers from some drawbacks, which limit the deployment of FSO links. The main drawback in FSO is the degradation in the signal quality because of atmospheric channel impairments. In addition, it is high sensitive for illumination noise coming from external sources such as sun and lighting systems. It is more benefit that FSO and mmWave are operating as a complementary solution that is known as hybrid FSO/mmWave links. Whereas the mmWave is susceptible to heavy rain conditions and oxygen absorption, while fog has no particular effect. This paper will help to better understand the FSO and mmWave technologies and applications operating under various atmospheric conditions. Furthermore, in order to improve the system performance and availability, several modulation schemes will be discussed. In addition to, the hybrid FSO/mmWave with different diversity combining techniques are presented.

In this paper, a threshold-based I-Q diversity combining scheme for ultra-high frequency (UHF) radio frequency identification (RFID) readers with a quadrature receiver is proposed in the aspect of improving the tag detection performance. In addition, the performance of the proposed scheme is evaluated as the closed-form expressions. In particular, its statistical characteristics are detailed and its performance is compared to that of conventional schemes over independent and identically distributed Rician fading conditions in terms of average signal-to-noise ratio (SNR), bit error rate (BER), and the average number of required combining process. Numerical results indicate that the proposed scheme enables processing power control through threshold control while meeting the required quality of service compared to conventional schemes.

In this letter, we consider a novel ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) structure, which consists of prerake diversity combiners in the transmitter and a zero forcing (ZF) detector in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and L resolvable multipath components, it is shown that the proposed prerake combining-based MIMO detection scheme has the diversity order of (LN-M+1) and its BER performance is analytically presented in a log-normal fading channel and also compared with that of a rake combining-based ZF scheme.

Both adaptive modulation and diversity combining are attractive techniques to combat fading and these two can be applicable to each digital-modulated symbol in OFDM transmission. In this letter, aiming to combat severe fading more effectively than the adaptive modulation, we theoretically analyze the benefit of a frequency diversity scheme within one OFDM symbol, which is a simple kind of coded OFDM (COFDM) based on IEEE 802.16 protocols. A simple closed form equation of bit error rate (BER) is derived, and then the advantages of correlated diversity gain and interference suppression by the diversity scheme are verified by both theoretical analysis and Monte Carlo simulation.

In inter-vehicle networks, it is required that collision warning messages be distributed over multiple hops with significantly short delay. Cut-through packet forwarding is known to be an effective method to reduce forwarding latency. However, it suffers from the reliability issue, which is especially severe in highly mobile scenario, due to multi-path fading. This paper tries to establish a reliable cut-through forwarding scheme by applying diversity combining method to collision warning messages. By exploiting the nature of the multi-hop forwarding of a broadcast packet in CDMA wireless networks, the diversity combining scheme does not incur any additional communication overhead or delay. The simulation results show that diversity combining schemes, especially Maximal Ratio Combining (MRC), can effectively reduce BER by orders of magnitude.

In our application targeted here, four on-glass antenna elements are set in an automobile to improve the reception quality of mobile ISDB-T receiver. With regard to the directional characteristics of each antenna, we propose and implement a joint Pre-FFT adaptive array antenna and Post-FFT space diversity combining (AAA-SDC) scheme for mobile ISDB-T receiver. By applying a joint hardware and software approach, a flexible platform is realized in which several system configuration schemes can be supported; the receiver can be reconfigured on the fly. Simulation results show that the AAA-SDC scheme drastically improves the performance of mobile ISDB-T receiver, especially in the region of large Doppler shift. The experimental results from a field test also confirm that the proposed AAA-SDC scheme successfully achieves an outstanding reception rate up to 100% while moving at the speed of 80 km/h.

In soft/softer hand-over of a wideband CDMA system, the RAKE receiver combines signals from different base stations by assigning separate fingers. A generalized maximal ratio combining technique for soft/softer hand-over is derived. Two correction schemes to optimize the MRC are proposed and compared against a conventional MRC.

Since Ultra Wideband Impulse Radio (UWB-IR) system can resolve many paths and is thus rich in multipath diversity, the use of Rake diversity combining is very effective. In the Rake diversity combining, the bit error rate (BER) is improved with the increase of the number of fingers. The Pre-Rake diversity combining is known as another technique to achieve the performance equivalent to the Rake diversity combining without increasing the receiver complexity. In the Pre-Rake diversity combining, the transmitted signals are scaled and delayed according to the delay and strength of the multipath. In this paper, we propose Pre-Rake diversity combining techniques for UWB systems, All-Pre-Rake (A-Pre-Rake) diversity combining using perfect channel information, Selective-Pre-Rake (S-Pre-Rake) diversity combining using the information on the L strongest paths, and Partial-Pre-Rake (P-Pre-Rake) diversity combining using the information on the first L paths. From the results of our computer simulation for UWB-IR systems in IEEE 802.15 UWB multipath channel model, we show that the proposed Pre-Rake diversity combining techniques are effective for the UWB-IR systems to achieve good error rate performance, while keeping the complexity of the receiver low. We also show that the S-Pre-Rake diversity combining is effective to achieve good error rate performance with less channel information.

A combining method for receiver diversity, followed by a Bayesian decision feedback equalizer, is proposed. This eigenvector based combining maximizes the desired part energy of combined channel, on which the equalizer performance mainly depends. The validity of the proposed method is demonstrated by simulations.

The bit error rate (BER) performance of a fast frequency-hopped frequency division multiple access (FH-FDMA) system is evaluated with diversity combining receivers. The clipper receiver and the normalized envelope detection (NED) receiver which show better performance than other diversity combining receivers under n = 1 band multitone interference (MTI) are chosen as combining alternatives. From simulation results, n = 1 band MTI is the most destructive multitone interference strategy for the FH-FDMA system. As the number of groups increases, eventually becoming a FHMA system, the worst case performance of FH-FDMA with the clipper receiver improves monotonically, while that of the NED receiver hardly improves when the effect of the interference is relatively large. From the viewpoint of BER performance, the FHMA system with the clipper receiver is the most effective solution among the FH-FDMA systems in the presence of the worst case band MTI.

In this paper, a modified Gardner's timing-error estimation algorithm is proposed for space-time block coding (STBC) schemes. In STBC schemes, the symbol timing-error can be estimated for each received antenna. The proposed algorithm is the diversity combining of all symbol timing-error estimates using Gardner's algorithm with the assumptions of identical channel delay of each SISO sub-stream. Simulation results show the proposed algorithm improves the symbol timing-error estimation performance through diversity gains. Estimation of symbol timing-error in multiple-input and multiple-output (MIMO) antenna systems is an another suitable area of application.

In fast frequency hopped (FFH) non-coherent MFSK systems, the diversity combining scheme can be used effectively in order to combat the interference, especially jamming noise. In this paper, we simulate and discuss the BER performance of FH/MFSK system for different diversity combining schemes, such as linear combining, clipped-linear combining, normalized envelop detection (NED), order statistics (OS) NED and product combining receiver (PCR), in the presence of both the worst case partial band jamming (PBJ) and the fading channel. The performances of those combining schemes except for linear combining are similar each other in the worst case PBJ without the fading. In the existence of both the worst case PBJ and the fading channel, the clipped-linear combining scheme suffers a larger drop in performance than other combining schemes. It is noteworthy that the performances of OSNED and PCR are the best in Rayleigh fading channel among those combining schemes.

The stage 3/2 decoding scheme, originally suggested by U. Timor, is modified for a Rayleigh fading channel to improve the performance of a fast frequency-hopped multiple access/multilevel frequency shift keying system. When signal-to-noise ratio per bit is 30 dB, the simulation results show that the modified stage 3/2 decoding scheme increases the spectral efficiency by 11% compared to the modified stage 1 decoding scheme at bit error rate of 10-3. Further, the performance comparisons are made between the modified multistage decoding scheme and the diversity combining methods, where the modified stage 3/2 decoding scheme shows better performance.

Maximal-ratio combining (MRC), which maximizes the carrier to noise ratio (CNR) of the combined signal, generally requires envelope detection and multiplication having linear characteristic over a wide dynamic range to generate a weighting factor for each branch. In this paper, we propose a simplified two-branch diversity combining scheme without linear envelope detection. The proposed scheme, called "level comparison weighted combining (LCWC),"is simplified in a manner that its weighting factor for each branch is generated from hard-decision results of comparing signal envelopes between two branches. Performance of LCWC is evaluated by computer simulation and laboratory experiment, which shows that its diversity gain is almost identical to that of MRC in a Rayleigh fading channel.

This paper describes the performance analysis of a distributed antenna system which includes space and path diversity with radio channel estimation. This system is used for CDMA personal communication systems. In this paper, the performance of a diversity system is analyzed precisely considering multipath and inter-antenna interference. In a diversity system, the adaptive RAKE receiver which estimates the characteristics of a radio channel adaptively has been used for diversity combining. In the adaptive RAKE, the time-variant characteristic has been approximated by a time function. In this paper, the estimation performance of the adaptive RAKE is analyzed in cases of time functions of 0-th, first and second degrees. The performances are evaluated and compared with the differential RAKE. The adaptive RAKE is found to improve the signal quality of more than 2dB in comparison with the differential RAKE. It is also found that the optimum parameter design can be achieved flexibly for radio channel estimation by using higher degree time functions.

We propose a direct-sequence spread-spectrum multi-access (DS/SSMA) receiver that incorporates multipath diversity combining and multistage co-channel interference (CCI) cancellation. This receiver structure which is more resistant to the near/far problem essentially removes more and more of the CCI with each successive cancellation stage. With the assumption that perfect channel estimates have been obtained, we analyze the bit error rate (BER) performance of this system when received powers are unequal. Results show that the BER can approach that of a single-user case as the number of CCI cancellation stages increases.