With the severe spectrum shortage in conventional cellular bands, millimeter wave (mmW) frequencies between 30 and 300 GHz have been attracting growing attention as a possible candidate for next-generation micro- and picocellular wireless networks. The mmW bands offer orders of magnitude greater spectrum than current cellular allocations and enable very high-dimensional antenna arrays for further gains via beamforming and spatial multiplexing. This paper uses recent real-world measurements at 28 and 73 GHz in New York, NY, USA, to derive detailed spatial statistical models of the channels and uses these models to provide a realistic assessment of mmW micro- and picocellular networks in a dense urban deployment. Statistical models are derived for key channel parameters, including the path loss, number of spatial clusters, angular dispersion, and outage. It is found that, even in highly non-line-of-sight environments, strong signals can be detected 100-200 m from potential cell sites, potentially with multiple clusters to support spatial multiplexing. Moreover, a system simulation based on the models predicts that mmW systems can offer an order of magnitude increase in capacity over current state-of-the-art 4G cellular networks with no increase in cell density from current urban deployments.

http://apps.fcc.gov/ecfs/document/view;NEWECFSSESSION=ThTmVg1SGvsFqgxGKYfckQC26BmBGYLH2jpL5z0dMms1j21m5YTC!-1110365353!-349327291?id=60001013324

Millimeter Wave Channel Modeling and Cellular Capacity Evaluation

Future generation cellular networks are expected to provide ubiquitous broadband access to a continuously growing number of mobile users. In this context, LTE systems represent an important milestone towards the so called 4G cellular networks. A key feature of LTE is the adoption of advanced Radio Resource Management procedures in order to increase the system performance up to the Shannon limit. Packet scheduling mechanisms, in particular, play a fundamental role, because they are responsible for choosing, with fine time and frequency resolutions, how to distribute radio resources among different stations, taking into account channel condition and QoS requirements. This goal should be accomplished by providing, at the same time, an optimal trade-off between spectral efficiency and fairness. In this context, this paper provides an overview on the key issues that arise in the design of a resource allocation algorithm for LTE networks. It is intended for a wide range of readers as it covers the topic from basics to advanced aspects. The downlink channel under frequency division duplex configuration is considered as object of our study, but most of the considerations are valid for other configurations as well. Moreover, a survey on the most recent techniques is reported, including a classification of the different approaches presented in literature. Performance comparisons of the most well-known schemes, with particular focus on QoS provisioning capabilities, are also provided for complementing the described concepts. Thus, this survey would be useful for readers interested in learning the basic concepts before going into the details of a particular scheduling strategy, as well as for researchers aiming at deepening more specific aspects.

/pdf/downlink-packet-scheduling-in-lte-cellular-networks-key-1z27kezket.pdf

Downlink Packet Scheduling in LTE Cellular Networks: Key Design Issues and a Survey

In this paper we propose a modification to Shannon capacity bound in order to facilitate accurate benchmarking of UTRAN long term evolution (LTE). The method is generally applicable to wireless communication systems, while we have used LTE air-interface technology as a case study. We introduce an adjusted Shannon capacity formula, where we take into account the system bandwidth efficiency and the SNR efficiency of LTE. Separating these issues, allows for simplified parameter extraction. We show that the bandwidth efficiency can be calculated based on system parameters, while the SNR efficiency is extracted from detailed link level studies including advanced features of MIMO and frequency domain packet scheduling (FDPS). We then use the adjusted Shannon capacity formula combined with G-factor distributions for macro and micro cell scenarios to predict LTE cell spectral efficiency (SE). Such LTE SE predictions are compared to LTE cell SE results generated by system level simulations. The results show an excellent match of less that 5-10% deviation.

LTE Capacity Compared to the Shannon Bound

Device-to-device (D2D) communication as an underlaying cellular network empowers user-driven rich multimedia applications and also has proven to be network efficient offloading eNodeB traffic. However, D2D transmitters may cause significant amount of interference to the primary cellular network when radio resources are shared between them. During the downlink (DL) phase, primary cell UE (user equipment) may suffer from interference by the D2D transmitter. On the other hand, the immobile eNodeB is the victim of interference by the D2D transmitter during the uplink (UL) phase when radio resources are allocated randomly. Such interference can be avoided otherwise diminish if radio resource allocated intelligently with the coordination from the eNodeB. In this paper, we formulate the problem of radio resource allocation to the D2D communications as a mixed integer nonlinear programming (MINLP). Such an optimization problem is notoriously hard to solve within fast scheduling period of the Long Term Evolution (LTE) network. We therefore propose an alternative greedy heuristic algorithm that can lessen interference to the primary cellular network utilizing channel gain information. We also perform extensive simulation to prove the efficacy of the proposed algorithm.

Efficient resource allocation for device-to-device communication underlaying LTE network

Embedding pico/femto base-stations and relay nodes in a macro-cellular network is a promising method for achieving substantial gains in coverage and capacity compared to macro-only networks. These new types of base-stations can operate on the same wireless channel as the macro-cellular network, providing higher spatial reuse via cell splitting. However, these base-stations are deployed in an unplanned manner, can have very different transmit powers, and may not have traffic aggregation among many users. This could potentially result in much higher interference magnitude and variability. Hence, such deployments require the use of innovative cell association and inter-cell interference coordination techniques in order to realize the promised capacity and coverage gains. In this paper, we describe new paradigms for design and operation of such heterogeneous cellular networks. Specifically, we focus on cell splitting, range expansion, semi-static resource negotiation on third-party backhaul connections, and fast dynamic interference management for QoS via over-the-air signaling. Notably, our methodologies and algorithms are simple, lightweight, and incur extremely low overhead. Numerical studies show that they provide large gains over currently used methods for cellular networks.

Cell Association and Interference Coordination in Heterogeneous LTE-A Cellular Networks

In this paper we investigate the potential of downlink frequency domain packet scheduling (FDPS) for the 3GPP UTRAN long-term evolution. Utilizing frequency-domain channel quality reports, the scheduler flexibly multiplexes users on different portions of the system bandwidth. Compared to frequency-blind, but time-opportunistic scheduling, FDPS shows gains in both average system capacity and cell-edge data rates on the order of 40%. However, the FDPS performance is shown to depend significantly on the frequency-domain scheduling resolution as well as the accuracy of the channel state reports. Assuming Typical Urban channel profile, studies show that the scheduling resolution should preferably be as low as 375 kHz to yield significant FDPS gain with two-branch receive diversity and in 20 MHz. Further, to have convincing FDPS gain the std. of error of radio state reports needs to be kept within 1.5-2 dB.

Performance of Downlink Frequency Domain Packet Scheduling for the UTRAN Long Term Evolution

In this paper we evaluate the performance of downlink channel dependent scheduling in time and frequency domains. The investigation is based on the 3GPP UTRAN long term evolution (LTE) parameters. A scheduler framework is developed encompassing frequency domain packet scheduling, HARQ management and inter-user fairness control. It is shown that by dividing the packet scheduler into a time-domain and a frequency-domain part the fairness between users can be effectively controlled. Different algorithms are applied in each scheduler part, and the combined performance is evaluated in terms of cell throughput, coverage, and capacity. We show that frequency-domain packet scheduling can provide a gain of around 35% in both throughput and coverage over opportunistic time-domain only scheduling. Furthermore, it is shown that by using an equal throughput scheduler, coverage can be improved by 100% at the expense of a 5% loss in average cell throughput in comparison with the proportional fair scheduler.

HARQ Aware Frequency Domain Packet Scheduler with Different Degrees of Fairness for the UTRAN Long Term Evolution

In this study we analyze the downlink OFDMA system level performance for three different channel quality indicator (CQI) reporting schemes. The effect of terminal measurement and estimation errors, quantization from formatting and compression, and uplink reporting delays and detection errors are included. We find that a simple threshold-based CQI scheme provides an attractive trade-off between downlink system level performance and uplink CQI signaling overhead, as compared to using a best-M scheme. When applied to the UTRAN LTE system in a 10 MHz bandwidth, we find that a frequency domain packet scheduling gain of 40% is achievable with a CQI word size of only 30-bits. Finally, the effect of applying a so-called outer loop link adaptation algorithm is reported.

Frequency Domain Scheduling for OFDMA with Limited and Noisy Channel Feedback

In this paper we investigate the performance of frequency domain packet scheduling (FDPS) under fractional load (FL), based on the UTRAN long term evolution downlink. Under FL, the packet scheduler does not need to transmit on entire system bandwidth due to lack of traffic in the network, which leads to an improvement in the user experienced SINR. System-level simulations show that the proportional fair scheduler tries to optimize resource allocation by avoiding transmission on frequencies that are experiencing severe interference. As an example, FDPS can provide a gain of 4 dB in SINR over the round-robin scheduler, when the load is equal to 25%. The observed interference control is achieved without any centralized management. Further, FDPS under FL can provide an effective trade-off between cell throughput and coverage. The FDPS performance is dependent on the ability of link adaptation to track variations in interference. This ability is reduced when the frequency usage pattern is changing rapidly over time.

A. Pokhariyal

Papers

LTE Capacity Compared to the Shannon Bound

Performance of Downlink Frequency Domain Packet Scheduling for the UTRAN Long Term Evolution

HARQ Aware Frequency Domain Packet Scheduler with Different Degrees of Fairness for the UTRAN Long Term Evolution

Frequency Domain Scheduling for OFDMA with Limited and Noisy Channel Feedback

Frequency Domain Packet Scheduling Under Fractional Load for the UTRAN LTE Downlink