• The Journal of the Acoustical Society of Korea
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• v.21 no.3
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• pp.230-236
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• 2002

A study on architecture of new parallel interference canceller which can be applied for reverse link of next generation mobile communication system supporting multi-rate is performed on this paper. The proposed method adopts new algorithm which can be applied for multi-rate system to reduce multiple access interference (MAI) which cause performance degradation of CDMA system and limit of channel capacity. The proposed system is evaluated by simulation results under various conditions. As a result, performance enhancement is achieved compared to existing conventional interference cancellers. Although the amount of calculation is increased, we can find that the performance is improved generally.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5C
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• pp.601-610
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• 2004

In this paper, the performance of an adaptive array antenna using Constant Modulus Algorithm (CMA) based on the signal structure for the IMT-2000 3GPP specification reverse link of an asynchronous direct sequence code division multiple access (DS-CDMA) system are evaluated. In addition, the performance is compared with the array antenna using Least Mean Square (LMS) based on the training signal. The simulation parameters such as the number of multipath, mu10pa1h intensity profiles between path, spreading gain and multiuser etc., are considered in the Monte Carlo simulation. Simulation results demonstrate an adaptive array antenna using CMA may give more capacity gain than the amy antenna using LMS in the case of multipath fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.1
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• pp.30-39
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• 1997

In this paper, a new practical coherent detection scheme for biorthogonal signals, which uses multi-symbol observation interval, is proposed and its performances are analyzed and simulated. The technique jointly estimates both the demondulated data and the channel from received signal only while reducing computation complexity by an approximate maximum-likelihood sequence estimation rather than symbol-by-symbol detection as in previous noncoherent detection. The scheme achieves performance close to that of ideal coherent detection with perfect channel estimates when select the appropriate observation symbol interval N in the given symbol alphabet wize M. What is particularly interesting is that the requeired average signal-to-noise ratio per bit ${\gamma}_{b}$ can be reducedd by as much as 1.4dB and the capacity can be increase by as much as 38% when we use this system in the CDMA cellular reverse link.

• Information and Communications Magazine
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• v.13 no.4
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• pp.56-63
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• 1996

In this paper, the phisical layer of 4.3008 Mcps wideband CDMA which is proposed as the standard of personal communication service system is introduced. It is designed to fit 5 MHz bandwidth by using $28{\times}2^n$ Hadamard code. 13 kbps CELP vocoder is chosen as the main one and 32 kbps ADPCM can be applied. In the reverse link, the burst pilot scheme is proposed and produces the increase of capacity compared with the continuous pilot method. In order to maintain the service quality when the signaling data is increased, the information data and signaling data are time-multiplexed and making use of signaling activity brings the increase of capacity. QPSK data and QPSK spreading, variable frame size, and code pair assignment for high data rate are accomplished and then information data is transmited up to 64 kbps. It is expected that the proposed techiniques here are used in the FPLMTS.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.665-675
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• 2001

In this paper, the reverse link performance of a imperfect power controlled DS/CDMA cellular system that uses a base station array antenna which can effectively remove the multiple access interference is analyzed considering both beam forming algorithm and power control error in shadowing. The blocking probability of the DS/CDMA cellular system based on array parameters, $E_b/N_o$ and statistics of interference is derived, and then the system capacity corresponding to a certain blocking probability is calculated. On the assumption that the blocking probability is set 1%, the system capacity using MCGM algorithm with 12 antenna arrays is more increased maximum 32 times than that using a omni-directional antenna and about 2 times than that using MMSE algorithm, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.957-966
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• 1998

In this paper an imrpoved Signal-to-Interference ratio(SIR)-based call admission control(CAC) algorithm for DS-CDMA cellular system is proposed and its performance is analyzed. This algorithm uses Residual-Capacity defined asthe additional number of initial calls that a base station can accept such that system-wide outage probability will guaranteed to remain below a certain level. the residual capcity at each cell is calculated according to the reverse-link SIR measured not only at the home cell but also the adjacent cells. Then the adjacent cell interference-coupling coefficient .betha. is used. In this work we propose an improved algorithm that .betha. varies according to the traffic load of the home cell. The influence of traffic condition on system performance, namely blocking probability and outage probability, is then examined via simulation. The performance of the improved algorithm is evaluated both under homogeneous and hot spot traffic loads. The results show that the improved algorithm outperforms conventional algorithms under all load values. Under over-load situation, especially, the improved algorithm gives almost constant outage performance the QoS(quality of service) can be guranted.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.4
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• pp.387-396
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• 2004

A scheme to evaluate the number of users and cell coverage of a WCDMA supporting multi-rate traffic is newly presented through calculation of the realizable Erlang capacity from a derived blocking probability and the path loss from the COST231 Walfisch-Ikegami(W) model. We evaluate the voice-data Erlang capacities at various data rates of 15 kbps to 960 kbps and it is shown that they have a linear relationship to each other. When the E$\_$b//N$\_$o/ is low from 4 ㏈ to 3 ㏈ in case of voice capacity of 50 Erlang at 8 kbps, the result shows the increase for the data capacity of 10 Erlang and the enlargement of 100 m for the cell coverage at low rate of 15 kbps, and the increase of 0.11 Erlang and the enlargement of 40 m at high rate of 960 kbps. The increase of the blocking probability results in the increase of the Erlang capacity, but not an effect on the cell coverage, and the increase of active users in a cell results in the decrease of the coverage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.762-769
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• 2007

Adaptive MIMO-OFDM (Orthogonal Frequency Division Multiplexing) system adaptively changes modulation scheme depending on feedback channel state information (CSI). The CSI feedback channel which is the reverse link channel has multiple symbol delays including propagation delay, processing delay, frame delay, etc. The unreliable CSI due to feedback delay degrades adaptive modulation system performance. This paper compares the MSE and data capacity with respect to delay and channel signal to noise ratio for the two multi-step channel prediction schemes, CTSBP and BTSBP, such that robust adaptive SISO-OFDM/MIMO-OFDM is designed over severe mobile multipath channel conditions. This paper presents an interpolation method to reduce feedback overhead for adaptive MIMO-OFDM and shows MSE with respect to interpolation interval.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.8-17
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• 2000

The BER performance and the capacity variation of a microcell due to power control error(PCE) is analyzed on service types(data and voice, respectively) for the reverse link of an overlaid cell CDMA system. The procedure of analysis is followed as: First, we calculate BER performance according to PCE. Next, we find the minimum SNR for voice service, BER=TEX>$10^{-3}$, and data service, BER=TEX>$10^{-5}$. Then, according to the calculated SNR, we find the maximum capacity of a microcell and macrocell and the capacity of a microcell where interference is considered is found and analyzed with that in perfect power control. We get to the results as follows. The BER performance in 1 dB PCE is similar to that in perfect power control, however, with a increase in PCE, the BER performance is largely degraded. In terms of capacity, it is shown that if the PCE is equal or less than 2 dB, the effect of the PCE on voice service is more than that on data service, but if the PCE is equal or more than 3 dB, effect of the PCE on data service is more than that on voice. Besides, if the PCE is equal or less than 2 dB, both PCE and interference should be considered to calculate the capacity of a microcell, but if the PCE is equal or more than 3 dB, interference can be negligible since the effect of PCE is much stronger than that of interference. Therefore, the microcell should be located where $R_d$, the ratio of a microcell to a macrocell radius, is equal to 0.1, and d, the ratio of the distance between a microcell and a macrocell to the macrocell radius, is equal or more than 0.5, in order to obtain a appropriate microcell capacity against interference. If $\sigma$ is adjusted to less than 2 dB, we may get equal or more than 70% of the maximum microcell capacity.