• Journal of KIISE:Information Networking
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• v.29 no.5
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• pp.466-472
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• 2002

We investigate the load sharing problem between the umbrella cell and the overlaid tells in hierarchical cell structure. A load sharing strategy is proposed and its performance is evaluated by simulation when it is used for transmission of the mobile Internet traffic using the High Speed Downlink Packet Access scheme. The results show that, with the proposed strategy, the microcell backs well the overlaid picocells up, especially when a specific picocell cluster suffers unusual heavy load condition. By using the strategy, we can reduce the installation cost, otherwise needed for increasing the system capacity of every picocell cluster to cope with the unusual heavy load.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.3
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• pp.36-47
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• 2003

Wideband Code Division Multiple Access (WCDMA) is one of the air interface techniques proposed for the third generation (3G) mobile communication system. WCDMA was selected because it fulfills the IMT-2000 requirements for higher data rate trans mission, support of multimedia capabilities and other flexible services due to its variable bit rates and larger bandwidth, improved capacity and coverage, efficient power control and support for advanced and improved detector structures. Performance evaluation of 3G wireless network through simulation plays an important role in the design and implementation of the actual system, aiding the wireless system designer by providing them the necessary performance conformance statistics prior to implementation. In accordance with this goal, a simulator engine was developed entirely on a MATLAB platform to emulate the behaviour of the WCDMA air interface for both the uplink and downlink in a real world fading mobile environment. This paper discuss the development of the simulator along with a brief description of its functionalities and user interface. The WCDMA air interface mode focused in this paper is in accordance to the 3GPPs frequency division duplex (FDD) mode and restricted to the physical layer description. Performance results for the selected cases for the downlink, uplink, varying mobile velocity and sampling rates are also provided.

• Journal of Korean Institute of Industrial Engineers
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• v.31 no.4
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• pp.349-357
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• 2005

The Adaptive Multi-Rate (AMR) speech codec is the mandatory for voice service in WCDMA systems. The AMR codec can be used efficiently to provide a balanced trade-off between the capacity and quality of voice by adjusting various service rates. In this paper, three ways of AMR mode allocation schemes on the downlink in WCDMA system are evaluated. To evaluate users satisfaction efficiently, new system performance measure and analytic models are proposed. The proposed analytic models can be applied to obtain optimal mode allocation ways while considering the system capacity and quality of voice. In numerical examples, the ways of finding optimal parameters are illustrated for the given traffic loads and the performances of three mode allocation schemes are compared.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.643-651
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• 2008

In this paper, we analyze the performance of normalized SNR based proportional fair scheduling with partial feedback information for multiuser MIMO-OFDMA systems. The closed form expression on the downlink capacity of the selective partial CQI feedback scheme is derived and its asymptotic behavior is investigated. From the performance analysis and numerical results, it is found that the optimal growth rate of downlink capacity can be achieved with bounded average feedback overhead irrespective of the number of users.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.4
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• pp.1424-1441
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• 2014

Two-tier femtocell networks, consisting of a conventional cellular network underlaid with femtocell hotspots, play an important role in the indoor coverage and capacity of cellular networks. However, the cross- and co-tier interference will cause an unacceptable quality of service (QoS) for users with universal frequency reuse. In this paper, we propose a novel downlink interference mitigation strategy for spectrum-shared two-tier femtocell networks. The proposed solution is composed of three parts. The first is femtocells clustering, which maximizes the distance between femtocells using the same slot resource to mitigate co-tier interference. The second is to assign macrocell users (MUEs) to clusters by max-min criterion, by which each MUE can avoid using the same resource as the nearest femtocell. The third is a novel adaptive power control scheme with femtocells downlink transmit power adjusted adaptively based on the signal to interference plus noise ratio (SINR) level of neighboring users. Simulation results show that the proposed scheme can effectively increase the successful transmission ratio and ergodic capacity of femtocells, while guaranteeing QoS of the macrocell.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.269-276
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• 2008

In this paper, we analyze the M-WiMAX UL capacity limits under 2-Tier cell layout, considering the effects of random user position, path loss models, fading channel and adjacent channel interference from WCDMA system. In order to make the analysis approximate to the practical system capacity, we propose a MCS-based capacity analysis method considering the effects of PER requirement and the utilized MCS levels in M-WiMAX system. The proposed MCS-based method is validated through a system-level Monte Carlo simulation. Furthermore, a comparison between the conventional Shannon method and the proposed MCS-based method is presented and the optimum cell radius is suggested.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.308-315
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• 2008

When operating in frequency-division duplex (FDD) mode, transmit beamforming in multiple-input single-output (MISO) wireless communication systems typically requires accurate knowledge of downlink channel state information (CSI) at the transmitter. In practical FDD systems, obtaining such downlink CSI at the transmitter is challenging, if not impractical. To circumvent such challenge and support user mobility, we present a new method for transmit beamforming based on simple beam-control commands (BCCs) in MISO FDD mobile systems. We then numerically evaluate the effects of BCC errors in terms of transmit power efficiency, system capacity, and outage probability.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.470-477
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• 2001

Multucarrier code-division multiple access(MC-CDMA) is one of the promising technique for high capacity wireless communication. Hower the carrier phase error and frequency offest cause the performance degradation of MC-CDMA due to the inter-carrier interference. In this work, downlink performance of the partially coherent MC-CDMA is analytically derived in Rayleigh fading channels. The bit error rate sensitivity by combining method, Maxiaml ratio combining (MRC)and Equal gain combining(EGC), is compared as functions of phase errors. multi-user interference, and received signal-to-noise ratio. The results show that the susceptibility for the performance degradation of EGc and MRC is negligible for loop SNR's of above 15 dB and above 10 dB, respectivtely.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.313-322
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• 2006

We consider a power controlled code division multiple access (CDMA) system with multiple flow types. At each of the N nodes, there are F flow types with different signal-to-interference-and-noise-ratio (SINR) requirements. To keep the complexity of the transmitter low, we assume that each node uses the same power level for all its flows. The single flow case has been fully solved and is well-understood. We concentrate on the multiple flow case, and use a novel and different approach. For the uplink problem with N = 2 and F arbitrary, the necessary and sufficient conditions to have a solution are found and proved. For the general N > 1 uplink problem, we provide a necessary condition for the problem to have a solution and an iterative algorithm to find the optimum solution. For the downlink case with F > 1 some properties of the optimal sequences are obtained.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.163-174
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• 2008

Performance of downlink transmission strategies exploiting cooperative transmit diversity is investigated for distributed multiple-input single-output (MISO) systems, for which geographically distributed remote antennas (RA) in a cell can either communicate with distinct mobile stations (MS) or cooperate for a common MS. Statistical characteristics in terms of the signal-to-interference-plus-noise ratio (SINR) and the achievable capacity are analyzed for both cooperative and non-cooperative transmission schemes, and the preferred mode of operation for given channel conditions is presented using the analysis result. In particular, we determine an exact amount of the maximum achievable gain in capacity when RAs for signal transmission are selected based on the instantaneous channel condition, by deriving a general expression for the SINR of such antenna selection based transmission. For important special cases of selecting a single RA for non-cooperative transmission and selecting two RAs for cooperative transmission among three RAs surrounding the MS, closed-form formulas are presented for the SINR and capacity distributions.