In this letter, we present a novel interference-aware clustering scheme for cell broadcasting service. The proposed approach is based on a genetic algorithm for re-clustering. Using the genetic algorithm, the suggested method efficiently re-clusters the user nodes when the relays fail in receiving the cell broadcasting message from the base station. The simulation results exhibit that the proposed clustering scheme can maintain much higher capacity than the conventional clustering scheme in the cases of relay outage. The re-clustering method based on genetic algorithm also shows lower complexity than the re-clustering approach based on exhaustive search.

Optical Code Division Multiplexing (OCDM) is a multiplexing technology for constructing future all-optical networks. Compared with other multiplexing technologies, it can be easily controlled and can establish lightpaths of smaller granularity. However, previous research has revealed that OCDM networks are vulnerable to cycle attacks. Cycle attacks are caused by multi-access interference (MAI), which is crosstalk noise on the same wavelength in OCDM networks. If cycle attacks occur, they disrupt all network services immediately. Previous research has proposed a logical topology design that is free of cycle attacks. However, this design assumes that path assignment is centrally controlled. It also does not consider the delay between each node and the centralized controller. In this paper, we propose novel logical topology designs that are free of cycle attacks and methods of establishing paths. The basic concepts underlying our methods are to autonomously construct a cycle-attack-free logical topology and to establish lightpaths by using a distributed controller. Our methods can construct a logical network and establish lightpaths more easily than the previous method can. In addition, they have network scalability because of their distributed control. Simulation results show that our methods have lower loss probabilities than the previous method and better mean hop counts than the centralized control approach.

Tunneling is one of the main methods for the transition from IPv4 to IPv6 networks. By encapsulating IPv6 packets in IPv4 or UDP packets, tunnels like 6to4, Isatap and Teredo provide a feasible way for IPv4 hosts to establish IPv6 connections to hosts in IPv6 internet or IPv6 islands. For IPv4 internet, the use of tunnels varies the traffic and increases the type of packets, making the network environment more complex. In addition to common tunnels, various types of tunnels with more layers are tested in this paper. The results of successful connections prove the usefulness of multi-layer packets with diverse layer-count and type on the internet. To ensure the security of internal networks, the influence on traffic analysis in dual-stack IDS devices caused by the diversity is studied. Three spoofing attacks of “data insertion”, “data evasion” and “attacks using UDP” are proposed to show the influence on IDS caused by tunnels. Compared to the attacks without tunnels, some constraining factors are eliminated, which may increase the security risk of IDS and decrease the attacker's difficulties. To summarize this kind of problem, the concept of “Tunnel Interference” is revealed. And as solutions to this problem, two methods, RA (Record All) and HEH (Hash for Each Header), are presented in this paper which theoretically solve these problems to a great extent. RA records all headers and compares from the outermost to innermost layer. HEH is hash-based and accumulates hash values of each header. Both of them have linear time and space complexity. Experimental results show that RA and HEH will lead to minor space increase and up to 1.2% time increment in each layer compared to the original dual-stack.

1 × N active multi-mode interferometer laser diode (MMI LD) is proposed and demonstrated to realize single-wavelength edge-emitter without using grating configuration. As the 1 × N active-MMI LDs are based on longitudinal mode interference, they have a potential of single-wavelength emission without incorporating any grating layer on/beneath active layer. The fabricated devices showed single-wavelength emission with a side mode suppression ratio (SMSR) of 12dB at a wavelength of 1.57µm.

This paper presents a VLSI design of a Tomlinson-Harashima (TH) precoder for multi-user MIMO (MU-MIMO) systems. The TH precoder consists of LQ decomposition (LQD), interference cancellation (IC), and weight coefficient multiplication (WCM) units. The LQ decomposition unit is based on an application specific instruction-set processor (ASIP) architecture with floating-point arithmetic for high accuracy operations. In the IC and WCM units with fixed-point arithmetic, the proposed architecture uses an arrayed pipeline structure to shorten a circuit critical path delay. The implementation result shows that the proposed architecture reduces circuit area and power consumption by 11% and 15%, respectively.

A subarray signal processing scheme is described for a large-scale two-dimensional analog-digital hybrid beamformer to be used in quasi-millimeter-wave-band mobile communication systems. Multiple analog phased arrays direct their respective beams to multiple users, enabling space-division multiple access (SDMA). An iterative soft-input soft-output (SISO) multi-user detector recovers multi-user signals from subarray output signals corrupted by inter-user interference (IUI). In addition, a phased-array directivity control algorithm is derived based on inter-subarray signal phase-difference estimation from inter-beam-interference (IBI)-cancelled subarray output signals. Simulation results demonstrate that our proposed scheme achieves reduced hardware complexity, IUI-resistant multi-user signal detection, and IBI-resistant multi-user-tracking phased-array directivity control.

The implementation and experimental evaluations of distributed zero-forcing beamforming (DZFBF) for downlink multi-user multiple-input multiple-output (DL MU-MIMO) systems are presented. In DZFBF, multiple access points (APs) transmit to own desired stations (STAs) at the same time and using the same frequency channel while mitigating inter-cell interference. To clarify the performance and feasibility of DZFBF, we develop a real-time transmission testbed that includes two APs and four STAs; all are implemented using field programmable gate array. For real-time transmission, we also implement a simple weight generation process based on ZF weight using channel state information which is fed back from STAs; it is an extension of the weight generation approach used in DL MU-MIMO systems. By using our testbed, we demonstrate the real-time transmission performance in actual indoor multi-cell environments. These results indicate that DL DZFBF is more effective than DL MU-MIMO with time division multiple access.

The multiple-input-multiple-output (MIMO) Gaussian wireless network with K users and an intermediate relay is investigated. In this network, each user with available local channel state information (CSI) intends to convey a multicast message to all other users while receiving all messages from other users via the relay. This model is termed the MIMO K-way relay channel with distributed CSI. For this channel, the sum capacity is shown as MK/(K-1)log(SNR)+o(SNR) where each user and the relay is equipped with M antennas. Achievability is based on the signal space alignment strategy with a K-1 time slot extension. A most general case is then considered, in which each user intends to recover all messages required within T time slots. We provide an improved scheme called fractional signal space alignment which achieves MK/(K-1) degrees of freedom in the general case and the feasibility condition is also explored.

This paper investigates a preprocessing technique for a multiuser MIMO downlink system. An efficient joint precoder design with adaptive power allocation is proposed by adopting the channel-diagonalization technique and the minimum mean square error (MMSE) criterion. By exploiting an MMSE-based decoder, we propose an iterative algorithm to design the precoder with further derived closed-form solutions for implementing adaptive power allocation. Simulation results verify the effectiveness of our proposed approach. Compared with conventional benchmark schemes, they show that our proposal matches the performance but with reduced computational complexity.

This letter investigates price-based power control for cognitive radio networks (CRNs) with interference cancellation. The base station (BS) of the primary users (PUs) will admit secondary users (SUs) to access by pricing their interference power under the interference power constraint (IPC). We give the optimal price for BS to maximize its revenue and the optimal interference cancellation order to minimize the total transmit power of SUs. Simulation results show the effectiveness of the proposed pricing scheme.

This work investigates the cell range expansion (CRE) possible with time-domain multiplexing inter-cell interference coordination (TDM ICIC) in heterogeneous cellular networks (HCN). CRE is proposed to enable a user to connect to a picocell even when it is not the cell with the strongest received power. However, the users in the expanded region suffer severe interference from the macrocells. To alleviate the cross-tier interference, TDM ICIC is proposed to improve the SIR of pico users. In contrast to previous studies on CRE with TDM ICIC, which rely mostly on simulations, we give theoretical analysis results for different types of users in HCN with CRE and TDM ICIC under the Poisson Point Process (PPP) model, especially for the users in the expanded region of picocells. We analyze the outage probability and average ergodic rate based on the connect probability and statistical distance we obtain in advance. Furthermore, we analyze the optimal ratio of almost blank subframes (ABS) and bias factor of picocells in terms of the network fairness, which is useful in the parameter design of a two-tier HCN.

Scheduling restriction is attracting much attention in LTE-Advanced as a technique to reduce the power consumption and network overheads in interference coordinated heterogeneous networks (HetNets). Such a network with inter-cell interference coordination (ICIC) provides two radio resources with different channel quality statistics. One of the resources is protected (unprotected) from inter-cell interference (hence, called protected (non-protected) resource) and has higher (lower) average channel quality. Without scheduling restriction, the channel quality feedback would be doubled to reflect the quality difference of the two resources. We present a simple scheduling restriction scheme that addresses the problem without significant performance degradation. Users with relatively larger (smaller) average channel quality difference between the two resources are scheduled in the protected (non-protected) resource only, and a boundary user, determined by a proportional fair resource allocation (PFRA) under simplified static channels, is scheduled on one of the two resources or both depending on PFRA. Having most users scheduled in only one of the resources, the power consumption and network overheads that would otherwise be required for the channel quality feedback on the other resource can be avoided. System level simulation of LTE-Advanced downlink shows that the performance degradation due to our scheduling restriction scheme is less than 2%, with the average feedback reduction of 40%.

As wireless LAN systems become more widespread, the number of access points (APs) is increasing. A large number of APs cause overlapping cells where nearby cells utilize the same frequency channel. In the overlapping cells, inter-cell interference (ICI) degrades the throughput. This paper proposes an interference-aware multi-cell beamforming (IMB) technique to reduce the throughput degradation in the overlapping cells. The IMB technique improves transmission performance better than conventional multi-cell beamforming based on a decentralized control scheme. The conventional technique mitigates ICI by nullifying all the interference signal space (ISS) by beamforming, but the signal spaces to the user terminal (UT) is also limited because the degree of freedom (DoF) at the AP is limited. On the other hand, the IMB technique increases the signal space to the UT because the DoF at the AP is increased by selecting the ISS by allowing a small amount of ICI. In addition, we introduce a method of selecting the ISS in a decentralized control scheme. In our work, we analyze the interference channel state information (CSI) and evaluate the transmission performance of the IMB technique by using a measured CSI in an actual indoor environment. As a result, we find that the IMB technique becomes more effective as the number of UT antennas in nearby cells increases.

This paper proposes a simple decentralized cell association method for heterogeneous networks, where low transmission-power pico or femto base stations (BSs) overlay onto a high transmission-power macro BS. The focus of this investigation is on the downlink and the purpose of cell association is to achieve better user fairness, in other words, to increase the minimum average user throughput (worst user throughput). In the proposed method, an appropriate cell association for all users within a cell is achieved in an iterative manner based on the feedback information of each individual user assisted by a small amount of broadcast information from the respective BSs. The proposed method does not require cooperation between BSs. Furthermore, the proposed method is applicable to cases of inter-cell interference coordination (ICIC) between macro and pico/femto BSs through the use of protected radio resources exclusively used by the pico/femto BSs. Based on numerical results, we show that the proposed method adaptively achieves better cell association for all users according to the user location distributions compared to the conventional cell range expansion (CRE) method. The advantage of the proposed method over CRE is further enhanced in an ICIC scenario.

Cognitive beamforming exploiting spatial opportunity is an attractive technique for secondary users to coexist with primary users in cognitive radio environments. If perfect channel state information of the interfering link is available, interference from a secondary transmitter to a primary receiver can be perfectly pre-nulled by choosing the ideal transmit beam. In practice, however, there is channel estimation error due to noise and the time-varying channels. To minimize the residual interference due to those channel estimation errors, channel prediction based on auto regressive (AR) model is introduced in this paper. Further, to cope with extremely rapidly-varying channels, a cognitive transmit power control technique is proposed as well. By combining channel prediction and transmit power control in cognitive beamforming, the cognitive users can share the spectrum with the primary users with a limited interference level in time-varying channels.

The heterogeneous network (HetNet), which deploys small cells such as picocells, femotcells, and relay nodes within macrocell, is regarded as a cost-efficient and energy-efficient approach to resolve increasing demand for data bandwidth and thus has received a lot of attention from research and industry. Since small cells share the same licensed spectrum with macrocells, concurrent transmission induces severe interference, which causes performance degradation, particularly when coordination among small cell base stations (BSs) is infeasible. Given the dense, massive, and unplanned deployment of small cells, mitigating interference in a distributed manner is a challenge and has been explored in recent papers. An efficient and innovative approach is to apply cognitive radio (CR) into HetNet, which enables small cells to sense and to adapt to their surrounding environments. Consequently, stations in each small cell are able to acquire additional information from surrounding environments and opportunistically operate in the spectrum hole, constrained by minimal inducing interference. This paper summarizes and highlights the CR-based interference mitigation approaches in orthogonal frequency division multiple access (OFDMA)-based HetNet networks. With special discussing the role of sensed information at small cells for the interference mitigation, this paper presents the potential cross-layer facilitation of the CR-enable HetNet.

Cell Range Expansion (CRE) is a promising technique for the enhancement of traffic offload to pico cells. CRE is realized by adjusting the trigger timing of handover (HO) toward/from pico cells. However, inappropriate setting of trigger timing results in HO failures or Ping-Pong HOs. Both the HO failures and the Ping-Pong HOs degrade the continuity of user data services. Therefore, when CRE is applied, both the HO failures and the Ping-Pong HOs should be kept suppressed in order to guarantee the continuity of services for users. However, in the conventional studies, the application of CRE is discussed without consideration of HO performance. This paper clarifies the application range of CRE from the perspective of HO performance by taking the HO failure rates and the Ping-Pong HO rates as HO performance measures. As an example, we reveal that there is an appropriate CRE bias values which keep both the HO failure rate and Ping-Pong HO rate less than 1%. Such an appropriate CRE bias value range is smaller than the one without consideration of HO performance, which is reported in the conventional studies. The authors also observed that Ping-Pong HO occurs due to the short staying time of users at pico cells in high velocity environment. The rate of such Ping-Pong HOs becomes more than about 1% when the user velocity is more than 60 km/h. Therefore, it is more difficult in high velocity environment than that in low velocity environment to find appropriate CRE bias values.

The interference rejection combining (IRC) receiver effectively improves the cell-edge user throughput by suppressing interference from the surrounding cells. The work item (WI) for the specification of the IRC receiver is now ongoing for Release 11 Long-Term Evolution (LTE)-Advanced. Furthermore, heterogeneous networks where low power nodes such as picocells are overlaid onto macrocells are important to further improve the system throughput per unit area. In heterogeneous networks, to achieve an offloading gain from macrocells to picocells, cell range expansion (CRE) is applied. Additionally, inter-cell interference coordination (ICIC) is applied to reduce the severe inter-cell interference imposed from the macrocells onto the sets of user equipment (UEs) connected to picocells. In such cases, the interference statistics are completely different from traditional well-planned macrocell deployments, which have been investigated for the IRC receiver. This paper clarifies the effect of the IRC receiver in a heterogeneous network employing CRE and ICIC. Simulation results show that when both CRE and ICIC are applied, the effect of the IRC receiver becomes small due to a reduction in the severe inter-cell interference from ICIC. However, we clarify that the user throughput gain at the cumulative distribution function of 5% from the IRC receiver exceeding 10% is achieved compared to the conventional minimum mean square error (MMSE) receiver in a heterogeneous network regardless of the usage of ICIC. Furthermore, in heterogeneous networks employing CRE and ICIC, we clarify that an average user throughput gain exceeding 5% is achieved from the IRC receiver and the improvement in the average user throughput is high especially for the UEs connected to picocells compared to UEs connected to macrocells.

In this paper, we propose four different strategies of node pair selection in multiple input multiple output (MIMO) interference channel where interference alignment (IA) is considered as a transceiver design method. In the first scheme, we consider the maximization of the sum rate by selecting node pairs in a brute force way. We also propose a sub-optimal sum rate maximization scheme with lower complexity than the first scheme. In the third scheme, we aim to minimize the number of links among pairs which incurs the outage in MIMO interference channel. In the fourth scheme, we suggest a max-min node pair selection scheme to enhance both the sum rate and the outage probability. Simulation results demonstrate that all our proposed node pair selection schemes can increase the sum rate but also while also reducing the outage probability compared to the scheme with random node pair selection.

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.