An ultra-wideband (UWB) system usually occupies a large frequency band, which may overlap with the spectrum of a narrow band system. The latter is referred to as a victim system. To effectively use frequency, a UWB system may create a notch in its spectrum to accommodate the victim signal for interference avoidance. Parameters of the notch such as the depth and the width of a notch need to be decided in accordance to victim systems. In this paper, we investigate the effective UWB avoidance by examining the suitable notch based on experimental evaluation. In the experiments, 3GPP LTE, Mobile WiMAX, as well as an IMT Advanced Test-bed are respectively employed to represent different types of victim systems. The UWB system is set up based on WiMedia specifications and operates at the UWB low band of 3.1–4.8 GHz. A notch is fabricated by nullifying the related subcarriers of the UWB signal. In addition, a filter or a window function is formed and employed to further smooth the notch. Bit error rate (BER) or packet error rate (PER) performances of victim systems are measured and used to evaluate the UWB interference. Our results show that when a notch is properly formed, the interference level introduced by UWB can be below the permitted level by regulations.

In order to support the increasing amount of mobile data traffic, Third Generation Partnership Project (3GPP) is actively discusses cell range expansion (CRE) and time domain multiplexing – inter-cell interference coordination (TDM-ICIC). They have shown to be attractive techniques for heterogeneous network (HetNet) deployment where pico base stations (BSs) overlay macro BSs. There are two control schemes of the TDM-ICIC. One, named ZP-scheme, stops radio resource assignments for data traffic in predetermined radio resources in the time domain (subframes). The other, named RP-scheme, maintains the resource assignment whereas it reduces the transmission power at macro BSs at predetermined subframes. In this paper, we clarify the effective ranges of both ZP-scheme and RP-scheme by conducting the system level simulations. Moreover, the appropriate power reduction value at predetermined subframes is also clarified from the difference in the effective range of various power reduction values. The comprehensive evaluation results show that both ZP-scheme and RP-scheme are not effective when the CRE bias value is 0 dB or less. If the CRE bias value is larger than 0 dB, they are effective when the ratio of predetermined subframes in all subframes is set to appropriate values. These values depend on the CRE bias value and power reduction in the predetermined subframes. The effective range is expanded when the power reduction in the predetermined subframes changes with the CRE bias value. Therefore, the effective range of RP-scheme is larger than that of ZP-scheme by setting an appropriate power reduction in the predetermined subframes.

In recent years, heterogeneous cellular network (HetNet) topology has been attracting much attention. HetNet, which is a network topology with low power base stations installed inside the cell range of conventional macrocells, can realize network capacity enhancement through the effects of macrocell offloading and cell shrinkage. Due to the heterogeneity nature of HetNet, network designers should carefully consider about the interference management, resource allocation, user association and cell range expansion. These issues have been well studied in recent literatures. However, one of the important problems which has not been well investigated in conventional works is the base station (BS) deployment problem in HetNet. This paper investigates the optimal pico base station deployment in heterogeneous cellular networks especially with the existence of hotspots. In this paper, pico BS locations are optimized together with other network parameters including spectrum splitting ratio and signal-to-interference-noise ratio (SINR) bias for cell range expansion to maximize the total system rate, by considering two spectrum allocation strategies, i.e. spectrum overlapping and spectrum splitting. Numerical results show that the optimized pico BS locations can improve the system rate, the average user rate and outage user rate in HetNet with hotspots.

This work studies the benefits of heterogeneous cellular networks with overlapping picocells in a large macrocell. We consider three different strategies for resource allocation and cell association. The first model employs a spectrum overlapping strategy with an SINR-based cell association. The second model avoids the interference between macrocell and picocell through a spectrum splitting strategy. Furthermore, picocell range expansion is also considered in this strategy to enable a load balancing between the macrocell and picocells. The last model is a hybrid one, called as fractional spectrum splitting strategy, where spectrum splitting strategy is only applied at the picocell-edge, while the picocell-inner reuses the spectrum of the macrocell. We constructs resource allocation optimization problem for these strategies to maximize the system rate. Our results show that in terms of system rate, all the three strategies outperform the performance of macrocell-only case, which shows the benefit of heterogeneous networks. Moreover, fractional spectrum splitting strategy provides highest system rate at the expense of outage user rate degradation due to inter-macro-pico interference. Spectrum overlapping model provides the second highest system rate gain and also improves outage user rate owing to full spectrum reuse and the benefit of macro diversity, while spectrum splitting model achieves a moderate system rate gain.

In order to improve the forward link capacity of cdma2000 HRPD (High Rate Packet Data) or CDMA2000 1xEV-DO, it is significant to overcome multi-path interference. This paper focuses on FDE (Frequency Domain Equalization) with MMSE (Minimum Mean Square Error) criterion. On top of that, backward compatibility with HRPD should be maintained, in other words common channels such as the pilot channel should not be changed. Thus, the PN (Pseudo Noise) spread pilot block without CP (Cyclic Prefix) signals has to be dealt with for FDE. However, this will cause the conventional channel estimation accuracy to deteriorate. In order to improve the estimation accuracy of the conventional method, this paper presents a MRC (Maximal Ratio Combining) spectrum estimator, IPI (Inter-Path Interference) canceller, and path searcher. The results obtained from computer simulations reveal that the proposed method can improve the PER (Packet Error Rate) performance significantly. If compared with Rake combiner and TDE (Time Domain Equalization) with NLMS (Normalized Least Mean Square) scheme, the maximum data rates at a fixed PER of 1% can be increased by 5 to 8 times and 1.25 to 2.67 times, respectively.

Effective and simply realizable rate compatible low-density parity-check (LDPC) codes are proposed. A parity check matrix is constructed with the progressively increased column weights (PICW) order and adopted to achieve a punctured LDPC coding scheme for a wide range of the code rates of the rate compatible systems. Using the proposed rate compatible punctured LDPC codes, low complex adaptive communication systems, such as wireless communication systems, can be achieved with the reliable transmissions.

This paper focuses on the MC-CDMA (Multi Carrier-Code Division Multiple Access) with the MMSEC (Minimum Mean Square Error Combining) receiver, which is a good candidate of a transmission scheme for beyond 3G systems. This paper evaluates the forward link capacity using the MMSEC receiver in the MC-CDMA cellular system, which employs TDM (Time Division Multiplex) transmission for multiple users. In this paper, the PDF (Probability Distribution Function) of the SINR (Symbol to Interference plus Noise energy Ratio) after MMSEC under multi-cell environment are calculated with the various number of the code division multiplexes. Based on the PDF, the numerical relation can be derived between the peak rate of the adaptive transmission and the average transmission rate per sector.

This paper proposes Twin Turbo (T2) MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing). The advanced iterative decoder, called the T2 decoder, decreases the transmission error rate compared to conventional turbo decoders because it uses the correlation information among the bits mapped on an identical symbol of multi-level modulation and updates the channel reliability. When T2 is applied to a MIMO-OFDM, the required symbol energy to noise power density ratio (Es/N0) can be reduced more effectively than when T2 is applied to SISO (Single Input Single Output). This is because T2 can use the correlation among the bits not only mapped on an identical symbol but also transmitted from different antennas. Moreover, T2 achieves good performance in a correlated MIMO channel because the average minimum squared Euclidean distances between symbol replica candidates consisting of signals transmitted from multiple transmitter antennas are reduced. Computer simulations verify that the required Es/N0 of T2 MIMO-OFDM using 16QAM is 1.9 dB lower than that of a conventional turbo decoder when the correlation coefficients of transmitter and receiver antennas are 0.8. A computational complexity analysis clarifies the relation between the increase in computational complexity and the reduction in the required Es/N0.

Aiming at actual evaluation of IMT-Advanced system performance using field tests, this paper develops an IMT-Advanced testbed system with a transmission bandwidth of 100 MHz. Taking into account recent advances in research and development of an IMT-Advanced system, orthogonal frequency division multiplexing (OFDM) with multiple-input multiple-output (MIMO) are also promising technologies in IMT-Advanced. In addition, in order to meet the requirements for IMT-Advanced, the system seems to have a bandwidth of about 100 MHz with the aid of MIMO transmission. The developed system is based on the above more reliable prediction compared with previous studies, and the goals of this development are to provide a more realistic transmission performance, judgment criteria for operators introducing new air interfaces, and to explore new applications. This paper also presents the experimental results of rotational OFDM (R-OFDM) and twin turbo (T2) decoder implemented in the testbed and demonstrates that our proposals are better than the conventional schemes in actual radio transmission. Both physical layer technologies have been proposed by the authors, however, the previous works are only predicated on computer simulation. In this paper, the proposals are experimentally evaluated by distorting the transmitted signal on radio waves with a fading simulator and additional noise generator. When the packet error rate performance is measured, the measurement results are verified to be in good agreement with the simulation results. The experimental results also demonstrate that the R-OFDM can reduce the required carrier to the interference power ratio (CIR) of OFDM by about 1.1 dB in single-input single output (SISO) multi-path fading channel. In addition, it becomes clear that the T2 decoder is better than the turbo decoder in error correction, and the required CIR reduction achieves about 0.8 dB in SISO AWGN channel. The throughput performances are also measured with different modulation and coding conditions, and the measured forward throughput in the SISO AWGN channel achieves up to 373.6 Mbps. In addition, by use of 22 MIMO transmission, the measurements results substantiate that throughput of 512.7 Mbps can be realized even in the multi-path fading condition.