Timo Nihtilä

IEEE 802.11ac: Enhancements for very high throughput WLANs

The IEEE 802.11ac is an emerging very high throughput (VHT) WLAN standard that could achieve PHY data rates of close to 7 Gbps for the 5 GHz band. In this paper, we introduce the key mandatory and optional PHY features, as well as the MAC enhancements of 802.11ac over the existing 802.11n standard in the evolution towards higher data rates. Through numerical analysis and simulations, we compare the MAC performance between 802.11ac and 802.11n over three different frame aggregation mechanisms, viz., aggregate MAC service data unit (A-MSDU), aggregate MAC protocol data unit (A-MPDU), and hybrid A-MSDU/A-MPDU aggregation. Our results indicate that 802.11ac with a configuration of 80MHz and single (two) spatial stream(s) outperforms 802.11n with a configuration of 40 MHz and two spatial streams in terms of maximum throughput by 28% (84%). In addition, we demonstrate that hybrid A-MSDU/A-MPDU aggregation yields the best performance for both 802.11n and 802.11ac devices, and its improvement is a function of the maximum A-MSDU size.

System performance of LTE and IEEE 802.11 coexisting on a shared frequency band

This paper presents the system performance analysis of 3GPP Long-Term Evolution (LTE) and IEEE 802.11 Wireless Local Area Networks (WLAN) in a situation where LTE downlink (DL) has been expanded over to unlicensed frequency band usually used by WLAN. Simple fractional bandwidth sharing mechanism is used to allow both technologies to transmit. The system performance is evaluated by means of fully dynamic network simulations.

Increasing Femto Cell Throughput with HSDPA Using Higher Order Modulation

In femto base station concept homes and small offices can be equipped with very low transmission power base stations to offer users high signal to interference and noise ratios (SINR) due to the close proximity of the base station unit. In the first release of high speed downlink packet access (HSDPA) specification the highest supported modulation scheme, 16 quadrature amplitude modulation (16QAM), might not be efficient enough to fully exploit the superior signal quality offered by the femto base stations making the use of a higher order modulation desirable. This paper presents a performance evaluation of using higher order modulation scheme, namely 64QAM, with HSDPA in a combined single frequency macro and femto cell scenario with advanced receivers used at mobile terminals. The impact of femto cells and 64QAM is also analyzed as a function of indoor user penetration. The analysis is done using dynamic system level simulations.

Capacity improvement by employing femto cells in a macro cell HSDPA network

Very low transmission power (femto) base stations can be used in small isolated areas with insufficient or no macro cell coverage to provide very high bit rates to users at close proximity of the base stations. In this paper the impact of femto cells operating on the same frequency as macro cells is evaluated in terms of several performance indicators in a realistically modeled single carrier HSDPA network by dynamic system level simulations. Conventional Rake and an advanced linear minimum mean squared error (LMMSE) equalizer receivers with and without receive diversity at the mobile terminals are considered. The results showed that co-channel femto cells offer considerable gains from both user and network perspective with all receivers even if the femto cell users are not concentrated near the femto base stations.

Performance Analysis of IEEE 802.11ac DCF with Hidden Nodes

Recently, the IEEE 802.11 standard based Wireless Local Area Networks (WLAN) have become more popular and are widely deployed. It is anticipated that WLAN will play an important rule in the future wireless communication systems in order to provide several gigabits data rate. IEEE 802.11ac is one of the ongoing WLAN standard aiming to support very high throughput (VHT) with data rate of up to 6 Gbps below the 6 GHz band. In the development of IEEE 802.11ac standard, several new physical layer (PHY) and medium access control layer (MAC) features are taken into consideration, such as employing wider bandwidth in PHY and incrementing the limits of frame aggregation in MAC. However, due to the newly introduced features, some traditional techniques used in previous standards could face some problems. This paper presents a performance analysis of 802.11ac Distributed Coordination Function (DCF) in presence of hidden nodes in overlapping BSS (OBSS) environment. The effectiveness of DCF in IEEE 802.11ac WLAN when using different primary channels and different frequency bandwidth has also been discussed. Our results indicate that the traditional RTS/CTS handshake mechanism faces shortcomings and needs to be modified in order to support the newly defined 802.11ac amendment.

HSDPA MIMO System Performance in Macro Cell Network

This paper studies the performance of dual-stream transmit antenna array (D-TxAA) technique in a macro cell high speed downlink packet access (HSDPA) network. 3rd generation partnership project (3GPP) responsible of the standardization of 3G systems selected D-TxAA as the multiple input-multiple output (MIMO) scheme for HSDPA in 3GPP specification Release 7. MIMO transmission doubles the theoretical peak data rate of HSDPA from 14.4 Mbps to 28.8 Mbps. However, successful reception of dual stream MIMO transmissions requires good signal conditions. Thus, employing MIMO is generally considered beneficial only in small cells due to the fact that in a macro cell network the channel conditions are seldom favourable to MIMO usage because the distances may be large between the base station and the mobile terminals. The objective of this paper is to study the actual impact of D-TxAA MIMO technique to user and system throughput in a macro cell HSDPA network. Using dynamic system simulations the performance of MIMO transmission is compared to a scenario where only conventional receive diversity is employed at the user entities.

Performance of LTE Self-Optimizing Networks Uplink Load Balancing

This paper presents a performance evaluation of an uplink load balancing algorithm for 3GPP Long-Term Evolution (LTE) Self-Optimizing/Organizing Networks (SON). The algorithm handles local overload situations in uplink by two different strategies: firstly passing load from overloaded cells to underloaded cells and secondly by controlling UL interference through UL power control (PC) parameter adjustment. The algorithm is distributed so it works independently in each eNodeB (eNB). Every eNB includes a specific SON module which takes various measurements from its own and the neighboring eNBs as an input and gives handover orders and parameter change commands to its designated eNB as an output. In the paper we present a description of the algorithm and evaluate its performance in a locally overloaded LTE network. The performance evaluation is done by the means of fully dynamic LTE system simulation tool comprising a detailed modeling of user equipment (UE) measurements, user mobility and handovers, traffic and radio resource management algorithms.

Performance of receive diversity and LMMSE chip equalization in WCDMA HSDPA network

More advanced receiver structures than the conventional single antenna Rake can be used to improve the signal-to-noise (SNR) ratios, which is especially beneficial in order to utilize the high bit rates provided by the HSDPA concept in Wideband Code Division Multiple Access (WCDMA) network. In WCDMA system, orthogonal Walsh–Hadamard sequences are used as channelization codes. In frequency-selective fading channels the orthogonality of channelization codes disappears and intra-cell multiple access interference (MAI) arises. In order to mitigate the effect of MAI, chip-level equalization has shown to be a simple and effective solution. The effectiveness of chip equalization, however, degrades at the cell borders where the inter-cell interference dominates rather than MAI. Dual antenna reception is a straight-forward solution to mitigate that performance drop. In this paper, we present an analysis of the expected gains of advanced receivers over conventional single antenna Rake receiver in realistic situations by using a dynamic WCDMA system-level tool. Considered advanced receivers include single and dual antenna Linear Minimum Mean Squared Error (LMMSE) chip-level equalizers and dual antenna Rake receiver. The network performance with advanced receivers is studied also from a more practical point of view by assuming that the penetration of advanced HSDPA terminal receivers is gradually increased in the network.

WCDMA HSDPA network performance with receive diversity and LMMSE chip equalization

More advanced receiver structures than the conventional single antenna Rake can be used to improve the signal-to-noise (SNR) ratios, which is especially beneficial in order to utilize the high bit rates provided by the HSDPA concept in WCDMA network. In WCDMA system, orthogonal Walsh-Hadamard sequences are used as channelization codes. In frequency-selective fading channels the orthogonality of channelization codes disappears and intra-cell multiple access interference (MAI) arises. In order to mitigate the effect of MAI, a chip-level equalization has shown to be a simple and effective solution. The effectiveness of chip equalization, however, degrades at the cell borders where the inter-cell interference dominates rather than MAI. Dual antenna is a straight-forward solution to mitigate that performance drop. In this paper we consider receivers equipped with dual antenna and linear minimum mean squared error (LMMSE) chip-level equalizers and present an analysts of the expected gains over conventional single and dual antenna rake receivers in realistic situations by using a dynamic WCDMA system-level tool

3G interworking with WLAN QoS 802.11e

Seamless interconnection with WLAN 802.11 and 3/4G technology is essential for the future wireless environment. Supporting quality of service is one of the most important issues in 3/4G. In this paper the WLAN QoS standard IEEE 802.11e draft is studied at the point access network for 3G traffic classes. 802.11e is compatible with the layer 2 802.11p standard and resembles DiffServ QoS functionality that is proposed to be one of the applied QoS standards in 3/4G networks. We analyze how well 802.11es QoS properties perform under the different kind of simulation scenarios when packet sizes and channel error rates are varied.