Beyond conventional cellular frameworks

Cooperative PSK constellation design and power allocation for massive MIMO uplink communications

In traditional half-duplex (HD) communication systems, the HD base station (BS) can transmit artificial noise (AN) to jam the eavesdroppers for securing the downlink (DL) communication. However, guaranteeing uplink (UL) transmission is not possible with an HD BS because HD BSs cannot jam the eavesdroppers during UL transmission. In this chapter, we investigate the resource allocation algorithm design for secure multiuser systems employing a full-duplex (FD) BS for serving multiple HD DL and UL users simultaneously. In particular, the FD BS transmits AN to guarantee the concurrent DL and UL communication security. We propose a multi-objective optimization framework to study two conflicting yet desirable design objectives, namely total DL transmit power minimization and total UL transmit power minimization. To this end, the weighted Tchebycheff method is adopted to formulate the resource allocation algorithm design as a multi-objective optimization problem (MOOP). The considered MOOP takes into account the quality-of-service (QoS) requirements of all legitimate users for guaranteeing secure DL and UL transmission in the presence of potential eavesdroppers. Thereby, secure UL transmission is enabled by the FD BS, which would not be possible with an HD BS. Although the considered MOOP is non-convex, we solve it optimally by semidefinite programming (SDP) relaxation. Simulation results not only unveil the trade-off between the total DL transmit power and the total UL transmit power, but also confirm that the proposed secure FD system can guarantee concurrent secure DL and UL transmission and provide substantial power savings over a baseline system.

As the number of people who own and use mobile telephones grows, more base stations are needed to carry the “traffic.” New features, enabled by the Third Generation Mobile Telecommunication System (“3G”) and Worldwide Interoperability for Microwave Access (“WiMAX”), such as internet access and multimedia services, require more and more information, or data, to be transmitted. The transmission of these large quantities of data increases the requirement for base stations.1 By mid-2007, there were over 50,000 wireless communication towers in Taiwan. Of these, about 26,000 were designed for the Second Generation Mobile Telecommunication System (“2G”), 6,000 for the 3G, and about 16,000 for the Personal Handy-phone System (“PHS”).2 Typically a wireless communication tower consists of an equipment cabinet, an antenna that sends and receives radio waves to and from mobile telephones, and a structure that supports the antenna.3 Each base station provides coverage for a given area. Base stations can be a few hundred meters apart in major cities or several kilometers apart in rural areas.4 The transmitting power of any particular base station is variable and depends on several factors, including the number of calls and the distance between the base station and the mobile telephone making the call. From a legal perspective, those “base stations,” “antenna” and “radio waves” are subject to substantive and procedural rules.5 This paper focuses on the conflict between operators and the community, common approaches used to regulate base stations and their associated problems, as well as the procedural issues of granting permission for cellular tower construction. After examining the regulatory framework for dealing with the construction of cellular towers, I propose some solutions. In particular, I analyze the issues from a procedural perspective, advocating a way forward that will help eliminate some of the problems caused by the conflict between the regulator, the telecommunications industry, and the local community. [1] In this article I use the terms “base station,” “cellular tower,” “wireless tower,” and “wireless communications tower” interchangeably. [2] The Public Statement of the Former Deputy Chief Commissioner of NCC, EPOCH TIMES, available at http://tw.epochtimes.com/bt/6/4/27/n 1300414.htm (last visited Oct. 20, 2008). [3] Office of Communications, Audit of Mobile Phone Base Stations – Information Sheet, http://www.ofcom.org.uk/sitefinder/audit-info (last visited Oct. 14, 2008). [4] Id. [5] See generally Jeffrey A. Berger, Efficient Wireless Tower Siting: An Alternative to Section 332(C)(7) of The Telecommunications Act of 1996, 23 TEMP. ENVTL. L. & TECH. J. 83 (2004). See also Robyn Durie, Challenges Faced in Providing Mobile Broadband Services, 11 COMPUTER AND TELECOMMUNICATION LAW REVIEW 66-72 (2005).

Integrated access and backhaul (IAB) network consists of base station (BS), relay nodes (RNs), and user-equipments (UEs), where BS and RNs exchange UE data via wireless in-band backhaul while sharing the same frequency-time resources with access links. In this paper, a flexible time-division-duplex (TDD)-based IAB network is considered where RNs and BS are assigned to distinct uplink (UL) or downlink (DL) transmission modes to mitigate conventional half-duplex (HD) loss at RNs. An iterative beamformer design is proposed to manage the resulting cross-channel interference and to allocate wireless backhaul and access resources jointly over two consecutive data delivery intervals required for communications between the BS and UEs through HD RNs. Dynamic traffic behavior is handled via weighted queue minimization objective, and user-specific UL/DL queues are also introduced at RNs to guarantee reliable end-to-end data delivery. Bi-directional forward-backward training via spatially precoded over-the-air pilot signaling is employed to allow decentralized beamformer design across all the nodes. A novel user allocation method is proposed to assign UEs to BS or RNs based only on long-term channel statistics and some practical IAB limitations. The numerical examples illustrate the superior system performance of the considered flexible IAB in comparison to the conventional HD relaying system.

The primary obstacles to high-speed communication, namely, shot noise from ambient light, high-capacitance photodiodes and multipath dispersion, are reviewed, and ways to counter them are demonstrated for a prototypical infrared system. The discussion is limited to the physical-layer issues involved in the design of a single high-speed optical link. The focus is on the downlink (from base station to portable), which is a more challenging problem technically than the uplink for two reasons. First, the complexity of the portable receiver is much more constrained than that of the base station, due to power consumption and cost restrictions. Second, the downlink data rates are likely to be much higher than the uplink rates, because downlink communication will include downloading large executable files and possibly video services, whereas uplink communication will be used for transferring working files and keyboard commands which tend to be much smaller.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper explores the potential application of simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR‐RIS) in improving the physical layer security (PLS) of millimetre wave (mmWave) non‐orthogonal multiple access (NOMA) uplink communications. In particular, the legitimate users on both sides of STAR‐RIS send confidential information simultaneously to the base station (BS) while keeping it secret from the eavesdroppers near the BS by exploiting the STAR‐RIS to proactively regulate the electromagnetic propagation environment. By jointly designing the transmit power, the active beamforming at the BS, and the reflecting/transmitting coefficients at the STAR‐RIS, the authors' goal is to maximize the minimum secrecy capacity subject to the successive interference cancellation decoding order constraints. Due to the non‐convexity of the formulated problem, an efficient algorithm is proposed by capitalizing on alternating optimization, a penalty‐based approach, successive convex approximation, and semi‐definite relaxation. Firstly, a two‐layer iterative algorithm based on the penalty for the joint beamforming optimization sub‐problem is proposed. Then, the non‐convex problem is transformed into a convex positive semi‐definite programming problem for the transmit power sub‐problem. Numerical simulation results reveal that the STAR‐RIS‐aided system has more tremendous advantages and effectiveness in improving the PLS of mmWave NOMA uplink communication compared with the benchmark schemes.

Millimeter wave (mmWave) communication with advanced lens antenna arrays is a promising technology for achieving cost-effective 5G wireless systems. This paper studies a multi-user mmWave single-sided lens multiple-input multiple-output (MIMO) system in the uplink communication, where the base station (BS) is equipped with a full-dimensional (FD) lens antenna array with both elevation and azimuth angle resolution capabilities, and each mobile station (MS) has the conventional uniform planar array (UPA). With limited radio frequency (RF) chains at the BS and one single RF chain at each MS, we propose a low-complexity path division multiple access (PDMA) scheme to enable virtually interference-free multiuser communications, by exploiting the angle-dependent energy focusing property of the lens antenna array at the BS as well as the multi-path sparsity of mmWave channels. Besides, a new technique called path delay compensation is proposed at the BS to effectively transform the frequency-selective MIMO channel to parallel frequency-flat small-size MIMO channels, for each of which the low-complexity single-carrier (SC) transmission can be applied. Numerical results show significant sum-rate gain with the proposed design over benchmark systems.

Energy harvesting techniques emerge as a potential solution for prolonging the lifetime of the energy-constrained mobile wireless devices. In this paper, we focus on radio frequency (RF) energy harvesting for multiuser multicarrier mobile wireless networks. The mobile users are capable of harvesting energy from the dedicated subcarriers over which they are communicating with the base station in addition to harvesting ambient RF signals. We propose a joint data and energy transfer optimization framework for powering mobile wireless devices through RF energy harvesting while minimizing the overall power consumption. The proposed framework determines the optimal power resources that need to be allocated to meet data rate requirements of downlink and uplink communications. Simulations show that substantial power savings are achieved by allowing the ambient RF energy harvesting as well as by exploiting the different system parameters.

셀룰러 시스템을 기반으로 하는 펨토셀 네트워크는 실내 환경에서 대용량 데이터 전송을 위한 기술로 주목 받고 있다. 본 연구에서는 다수의 펨토 기지국을 배치하여 서비스를 제공하는 실내 환경에서 커버리지 문제와 데이터 전송 부하 문제를 동시에 고려하는 기지국의 파워 조절 분산 방법을 제안한다. 사용자의 데이터 사용량은 시간과 장소에 따라 지속적으로 변화하기 때문에 기지국의 데이터 전송 부하를 효과적으로 분배하는 동적 파워 조절 방법이 요구된다. 또한, 대규모 시설에 설치되어 있는 펨토셀 네트워크 시스템을 효율적으로 운영하기 위해서는 기지국의 파워 조절을 위한 분산 알고리즘이 필요하다. 본 논문에서는 기지국 사이의 데이터 전송 부하를 효과적으로 분배하는 분산 알고리즘을 제시한다. 또한, 일부 기지국에서 발행한 장애를 대응하는 방법과 새로운 기지국을 추가하는 방법을 제시한다. 모의 실험을 통해서 제안한 알고리즘의 성능을 시험하였다.

In this paper, we study the degrees of freedom (DoF) of cellular networks in which a base station with full-duplex operation simultaneously communicates to multiple half-duplex mobile stations. The half-duplex mobile stations are assumed to either communicate with the base station in the uplink or downlink. For such networks, inter-terminal interference needs to be taken into account to achieve the potential gain that doubles the throughput of conventional half-duplex cellular networks. We provide an achievable total DoF for such networks and show that having full-duplex operation at the base station only can indeed double the DoF when the number of mobile stations is sufficiently greater than the number of antennas at the base station. The key idea is to utilize the full DoF for the uplink transmission, while minimizing the inter-terminal interference via interference alignment. The downlink communication rate is then carefully chosen to occupy the remaining DoF at the receiving mobile stations.

Positioning of users or mobile station (MS) in cellular systems becomes an interesting topic since the related number of applications for the location information is growing rapidly. The decision to make the locating of mobile phones under the US Federal Communications Commission (FCC) mandatory is one of the driving forces to research and provide solutions to it. Deploying such applications would require a proper method for positioning the MS that are simple and accurate especially in urban area. There are many research papers addressing this issue based on timing method that calculate the timing delay for signal sent from MS to base station (BS) or vise versa, and other method based on signal strength. In this paper, we present a new calculation method to locate the mobile phone in urban district. This technique is based on hybrid method that uses signal strength to estimate the timing delay and comparing it with the measured time of arrival of the signal. The minimum timing value of the two results would be accepted and averaged for n samples. This will improve the accuracy and reduce the effect of multi-path signaling that both timing signaling and signal strength methods suffer from. In addition, a new calculation method has been presented to find the location of MS based on the BSs coordinates.

The proliferation of network devices and novel bandwidth hungry applications over the existing network imposes novel challenges in terms of fulfilling the users&#x2019; requirements. Dense deployment of small cells is thought to be a promising solution to fulfill these requirements. However, the user association in such dense networks becomes challenging and can greatly affect the network performance, as a user in such dense deployments can be connected to any of the available base stations. Traditionally, the user association has been performed based on the signal strength, however, such an approach does not apply when taking into account novel bandwidth hungry applications. Moreover, in recent years, a successful paradigm has been proposed to handle such bandwidth hungry applications, i.e., caching at small cell base stations. In this paper, we aim to solve this joint problem of user association and content caching in a dense small cell setting. To solve this problem, we present a novel iterative scheme that uses matching theory and a learning approach to find a suboptimal solution of the joint NP hard problem. Note that the user association and cache placement are strongly coupled, i.e., the association of users at a base station will determine the cache placement at base stations and the availability of cache at base stations will force the users to change their associations. Simulation results show that the proposed scheme (i.e., cache aware user association) significantly outperforms the cache unaware scheme and achieves a performance gain of up to 31&#x0025; in terms of normalized utility and saves up to twice the backhaul bandwidth. Moreover, the proposed scheme also achieves up to 82&#x0025; of the utility obtained by the optimal solution.

We study the performance of a single-cell massive multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system that uses linear precoding to serve multiple users on the same time-frequency resource. To minimize overhead, the channel estimates at the base station are obtained via comb-type pilot tones during the training phase of a time-division duplexing system. Polynomial regression is used to interpolate the channel estimates within each coherence block. We show how such regressors can be designed in an offline fashion without the need to obtain channel statistics at the base station, and we assess the downlink performance over a wide range of system parameters.

To deal with challenges of enhanced user density, high data rate demand and coverage, conventional macro cellular network architecture is evolving to irregular and complex Heterogeneous Networks (HetNets) through dense deployment of low power Base Stations (BSs) such as pico and femto BSs. Various parameters and their effects are considered while analyzing the performance of HetNets. In this paper we investigate the impact of macro and pico BSs separation on the network performance. We consider picocell within the association region of a macrocell and investigate the association region of picocell, average rate, and Energy Efficiency (EE) of the network. The results show that network performance is improved with increase in macro and pico BSs separation within the association region of a macrocell.

The problem of uplink communications is considered where multiple mobile terminals equipped with multiple antennas are communicating with one base station also having multiple antennas. A theory for jointly optimizing the transmitter and receiver finite impulse response (FIR) multiple-input multiple-output (MIMO) filters is developed. The signals from the individual users are assumed to be uncorrelated with each other and the additive channel noise is uncorrelated with the original signals. The FIR MIMO channel filters are assumed to be known for both the mobile terminals and the base station. All the input signals to the FIR MIMO channels are assumed to be power-constrained. For given FIR MIMO channels with maximum allowable average input powers, the transmitter and receiver FIR MIMO filters are jointly optimized such that the mean square error (MSE) between the desired and reconstructed signals is minimized. An iterative numerical optimization algorithm is proposed. Numerical simulation results show that the proposed method has substantially better performance than a code division multiple access (CDMA) based system using minimum MSE receiver filters.