Niclas Wiberg

Uplink admission control in WCDMA based on relative load estimates

When operating a cellular radio system at nearly full capacity, admitting yet another user may jeopardize the stability of the system as well as the performance of the individual users. Therefore, proper admission control is crucial. Prior art includes algorithms which limit the number of users or the uplink interference per cell. Both are known to yield roughly the same performance, but the former is difficult to configure, and the latter is based on a quantity which is hard to measure accurately. The core idea in this work is to predict the relative load of the system directly, given that a user is admitted. Then, the user will be admitted if the predicted load in the specific cell, and in its neighbors, is below some threshold. The proposed uplink relative load estimate is focused on WCDMA. It utilizes measurements readily available in that system, either periodically scheduled or from handover events. Multi-services are naturally handled, and availability of high data-rate services are automatically limited with respect to coverage, compared to services of lower data-rate. Simulations indicate that the admission control operates satisfactorily in different traffic situations with a universal parameter setting. Furthermore, the reporting overhead with periodical measurements can be avoided, since handover event-driven measurements yield roughly the same performance.

Streaming applications over HSDPA in mixed service scenarios

High-speed downlink packet access (HSDPA) is included in release 5 of the WCDMA specifications to increase downlink capacity and bitrates. This paper considers performance aspects of streaming applications over HSDPA in a mixed streaming and best-effort service scenario. Different scheduling algorithms are evaluated with the aim of providing sufficient quality-of-service for streaming. The simulation results show that reasonable streaming performance can be achieved without service differentiation if a somewhat fair scheduler is used, and that a streaming-aware scheduler further can protect streaming quality-of-service in high load conditions.

A future radio-access framework

This paper discusses the requirements on future radio access and, based on the requirements, proposes a framework for such a system. The proposed system based on orthogonal frequency-division multiplexing supports very low latencies and data rates up to 100 Mb/s with wide area coverage and 1 Gb/s with local area coverage. Spectrum flexibility is identified as one main requirement for future systems, and the proposed framework can be deployed in a wide range of spectrum allocations with bandwidths ranging from 2.5 to 100 MHz. Multihop relaying, useful to extend the range for the high data rates, and multiple-antenna configurations are integral parts of the framework. A packet-centric approach is taken for the dataflow processing, implying that the scheduling mechanism and the retransmission protocol operate on complete packets rather than segments thereof, thus allowing for cross-layer optimization. Finally, numerical evaluations are provided, illustrating the feasibility of future very wideband radio access.

Scheduling algorithms for HS-DSCH in a WCDMA mixed traffic scenario

Several scheduling algorithms are evaluated for the HS-DSCH channel in a WCDMA mixed traffic scenario. The traffic consists of FTP and Web surfing users. The maximum channel quality indicator (CQI) scheme serves users with the highest channel quality. The proportional fairness (PF) scheme tends to be fairer by prioritising users with higher channel quality (lower throughput). The weighted-queue-PF prioritises users with higher channel quality, lower throughput and those with longer queued-time. The results depict that the maximum system throughput is achieved by max CQI scheduling, which is pinch channel dependent. The max CQI scheme is also relatively fair to the FTP users. In case of Web surfing users, the proportionally fair scheduling is as good as the other schemes for the 10% worst users.

Machine-to-machine communication with long-term evolution with reduced device energy consumption

We present a method to reduce the device battery consumption to efficiently support battery-operated machine-to-machine (M2M) communication in 3GPP long-term evolution. The long-term evolution discontinuous reception (DRX) is a key mechanism in reducing the device energy consumption, and we discuss how the traffic behaviour of machines in the Internet of things scenarios differs from the typical cellular user of today, for whom the current DRX mechanism is optimised for. We list typical transactions in M2M scenarios and discuss how the DRX operation is affected. We continue by introducing a power consumption model for M2M devices. Our assumption is that the device transmits small amounts of data in the uplink with deterministic intervals. The model takes into account the energy consumption in the active and the nonactive periods of the communication, which alternate depending on the DRX configuration. We use the model with different parameter settings referring to potential future M2M devices and identify the parameters, which contribute most to the device energy consumption. The results indicate that making the current maximum DRX cycle length longer will lead to significant gains in the energy consumption of M2M devices compared with what is possible today. Our key contributions include the discussion of the DRX mechanism in the Internet of things scenarios and the realistic assumptions for the potential of trading the responsiveness of a device for energy consumption gain with very long DRX cycles. Copyright

Reducing energy consumption of LTE devices for machine-to-machine communication

We present a method to reduce the device battery consumption to efficiently support machine-to-machine (M2M) communication in LTE. We first introduce a model for calculating energy consumption of a LTE device. We assume that the M2M device transmits small amounts of data with deterministic intervals. Our model takes into account the energy consumption in active and nonactive periods which alternate depending on the configuration of discontinuous reception (DRX). We use the model with different parameter settings referring to potential future M2M devices. The results indicate that making the current maximum DRX cycle length longer would lead to significant gains in the energy consumption of M2M devices. Thus, our key contribution is to show the potential of trading the responsiveness of a device for energy consumption gain with very long DRX cycles.

Analysis of a CDMA downlink in multipath fading channels

This paper deals with the performance analysis of a CDMA downlink in multipath fading channels. An approximate expression for the demodulated signal-to-noise ratio is developed for a conventional RAKE receiver. The expression includes an orthogonality factor that quantifies the performance gain of using orthogonal spreading codes in the presence of a time-dispersive channel. A comparison with simulation results shows that the accuracy of the expression is high in various combinations of desired signal, orthogonal and non-orthogonal intra-cell interference, and AWGN. The numerical results also show that not only the strength of individual rays but also their relative phases and delays determine the value of the orthogonality factor.

Comparison of Strategies for Signaling of Scheduling Assignments in Wireless OFDMA

This paper considers the transmission of scheduling information in orthogonal frequency-division multiple-access (OFDMA)-based cellular communication systems such as the Third-Generation Partnership Project (3GPP) long-term evolution (LTE). These systems provide efficient usage of radio resources by allowing users to be dynamically scheduled in both frequency and time. This requires considerable amounts of scheduling information to be sent to the users. This paper compares two basic transmission strategies: transmitting a separate scheduling message to each user versus broadcasting a joint scheduling message to all users. Different scheduling granularities are considered, as are different scheduling algorithms. The schemes are evaluated in the context of the LTE downlink using multiuser system simulations, assuming a full-buffer situation. The results show that separate transmission of the scheduling information requires a slightly lower overhead than joint broadcasting when proportional fair scheduling is employed and the users are spread out over the cell area. The results also indicate that the scheduling granularity standardized for LTE provides a good tradeoff between scheduling granularity and overhead.

Improved Error Protection for Uplink Control Signaling in 3GPP-LTE via Complex-Field Coding

We study the uplink control signaling in 3GPP-Long Term Evolution (LTE) systems. Specifically, we propose a precoding method that uses complex-field coding (CFC) to improve the performance of the PUCCH format 2 control signaling. In the case of perfect channel state information (CSI) at the receiver and with a single receive antenna, the proposed method offers significant gains compared to the coding currently used in 3GPP-LTE. However the gains are marginal with two receive antennas. In order to examine the impact of channel estimation errors, we also derive the optimal detector for the case of imperfect receiver CSI, both for conventional coding and for the proposed CFC method.

On Coding of Scheduling Information in OFDM

Control signaling strategies for scheduling information in cellular OFDM systems are studied. A single-cell multiuser system model is formulated that provides system capacity estimates accounting for the signaling overhead. Different scheduling granularities are considered, including the one used in the specifications for the 3G Long Term Evolution (LTE). A greedy scheduling method is assumed, where each resource is assigned to the user for which it can support the highest number of bits. The simulation results indicate that the cost of control signaling does not outweigh the scheduling gain, when compared with a simple round-robin scheme that does not need signaling of scheduling information. Furthermore, in the studied scenario, joint coding and signaling of scheduling information over all selected users is found to be superior to separate coding and signaling for each user. The results also indicate that the scheduling granularity used for LTE provides better performance than the full granularity.