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Optimized Outer Loop Power Control Technique on Circuit Switched Service in Wideband Code Division Networks

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Optimized Outer Loop Power Control Technique on Circuit Switched Service in Wideband Code Division Networks
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  Islamic University Multidisciplinary Journal Vol. 6 Issue 2, June, 2019 268 Optimized Outer Loop Power Control Technique on Circuit Switched Service in Wideband Code Division Networks 1 Ukhurebor K.E, 2 Maor M.S., 3 Aigbe E.E, 4 Ukagwu K.J. 1,2 Department of Physics, Edo University Iyamho, Nigeria   3 LM Ericsson, Victoria Island, Nigeria   4 School of Engineering and Applied Sciences, Kampala International University, Uganda   1 ukhurebor.kingsley@edouniversity.edu.ng or  ukeghonghon@gmail.com;  2 moses.maor@gmail.com,  3  jefosaaigbe@gmail.com,  4 ceekay2yk@yahoo.com  Abstract  Interference is a serious challenge for cellular wireless systems; this is one of the main reasons why there has been a great attention by the management of any cellular network service provider to the reduction of interference effects on their network systems in order to procure sufficient and better quality of service. In this study the Optimized Outer Loop Power Control technique was applied to reduce interference in order to improve the quality of circuit switched services in Wideband Code Division Multiple Access (WCDMA) wireless cellular network. It is obvious that WCDMA system is not yet ubiquitously in Nigeria and most developing countries of the world, owing to the amount of new infrastructures required in it. By using this technique, the performance of circuit switched quality of service will be improved through the simulated results. Hence, the quality of service of both Narrow Band and Wide Band Adoptive Multi Rate (AMR) samples of WCDMA wireless cellular network will be greatly enhanced and this can also be used as a strategy to optimize the quality of circuit switched service of the network generally. It is recommended that this technique should be adopted for wireless network operators using WCDMA access technology so as to improve the quality of services of circuit switched and maximize profit.   Keywords: Interference; Signal; Users Equipment; Uplink; QoS   Introduction  Managing the medium of transmission of signals in cellular network systems is somehow difficult because of interference wave and noise problems. Interference disrupts the signal as it travels along the channel generating unwanted signals to the useful signal (Mohan and Travichandran, 2012; Ukhurebor et al ., 2017; Jraifi  et al ., 2010; deCarvalho and Madureira, 2001). In cellular network systems, interference is one of the most common problems in the Radio Access Network (RAN); this is because RAN is the part of the network that deals with the air interface. It is a serious challenge for wireless cellular network systems; this is one of the main reasons why there has been a great attention by the management of any cellular network service provider to the reduction of interference effects on their cellular network systems in order to procure sufficient and better Quality of Service (QoS) for their subscribers (Ukhurebor  et al ., 2017; Jraifi  et al ., 2010; deCarvalho and Madureira, 2001; Lawal  et al ., 2016; Ukhurebor and Aigbe, 2016; Ukhurebor  et al ., 2015; Ukhurebor  et al ., 2015).   WCDMA system which is a Third Generation (3G) Network has been fully deployed in developed countries of the world. However, owing to the amount of new infrastructures required, it will still need some time before this technology is ubiquitous in most developing countries like Nigeria (deCarvalho and Madureira, 2001; Lawal  et al ., 2016; Ukhurebor and Aigbe, 2016; Ukhurebor  et al ., 2015; Ukhurebor  et al ., 2015; Lina et al ., 2011). WCDMA system is a self-interference system; Internal Interference System (IIS). The capacity and performance of any WCDMA system is mainly affected by the following kinds of interference:   i).   Multiple Access Interference (MAI) or Inter User Interference (IUI) ii).   Inter-Symbol interference (ISI)   iii).   Near-Far Interference (NFI)    ISSN: 2617-6513 (Online), ISSN: 2409-0263 (Print) 269 The higher the number of subscribers added per sector, the higher the traffic load (primarily, due to data upsurge) in a cellular wireless mobile network that uses WCDMA system, and the greater the risk of problems caused by interferences which translates into poor QoS (deCarvalho and Madureira, 2001; Lina et al ., 2011). In WCDMA systems the major causes and sources of interference are; another mobile in the same cell and a call in progress in the neighboring cell. Others causes and sources of interference that are not prominent in WCDMA systems are; other base stations operating on the same frequency and any non-cellular system which leaks energy into the cellular frequency band. Cell sites are normally subjected to internal interference caused by the improper conductivity of passive devices such as connectors, cables, or antennas, even though if the different wireless systems do not generate harmonics, frequency drifts or radio frequency (RF) leakage. This internal interference can generate inter-modulation signals at the same frequency band as mobile transmitters (Uplink). Another common case of interference internal to the RAN is caused by frequency re-farming. In a bid to efficient spectrum management, Network service providers evolving their system technology to use Global System of Communication (GSM) and WCDMA technologies together on the same spectrum (GU at 5M Re-farm) use re-farming to deliver higher throughput for mobile devices while maintaining their existing technologies such as GSM and WCDMA. This technique supports a gradual adoption of WCDMA on GSM spectrum band. The co-existence of multiple technologies in a limited spectrum is forcing wireless cellular network providers to increase the number of carriers and to re-use frequencies hereby creating a RAN subject to internal interference. Inter-modulation in passive components is created when two signals are transmitted in a cabling system with improper conductivity characteristics such as loose jumpers, bent cables, different metals in jumpers, or corrosion. This inter modulation generates signals as products or multiples of the two transmitted signals (deCarvalho and Madureira, 2001; Mariappan et al ., 2016; Owen et al ., 2000).   On a broad level, there are two approaches to tackle and reduce interference in WCDMA system. These are:   i).   Power Control Approach and   ii).   Interference Cancellation Approach   Power Control Approach is one of the most important mean of reducing this interference because controlling the power transmission on the uplink channels can help in reducing the amount of interference caused to other users (deCarvalho and Madureira, 2001; Lina et al ., 2011; Owen et al ., 2000). Power Control is performed by the Universal Mobile Terrestrial System (UMTS), UMTS Terrestrial Radio Access Network (UTRAN) to adjust and control the power of transmitting signals according to changes of the channel environment and quality of received signals. The purpose of Power Control is to minimize the transmit power while ensuring the service quality. Power Control can be divided into Inner Loop Power Control (ILPC) and Outer Loop Power Control (OLPC).   i).   Inner  –  Loop Power Control (ILPC) determines whether the difference between the uplink Signal to Interference Ratio (SIR) and the SIR target is decreasing and adjusts the transmit power of Users Equipment (UEs) based on the difference.   ii).   Outer-Loop Power Control (OLPC) determines whether the difference between the uplink Block Error Rate (BLER) and the target BLER is decreasing and adjusts the SIR target based on the difference. The adjusted target SIR is sent to the RNC for ILPC.   In this study the Outer-Loop Power Control (OLPC) was adapted in order to reduce the interference in a wireless cellular network service in Nigeria that uses WCDMA system so as to improve the quality of circuit switched services.  Materials and Methods When calculating the Uplink BLER for OLPC, if the network controller receives incorrect voice frames, it increases the target SIR promptly; if the Controller receives correct voice frames, it  Islamic University Multidisciplinary Journal Vol. 6 Issue 2, June, 2019 270 decreases the target SIR slowly to avoid ping-pong effect. However, the target SIR remains unchanged for UEs that are performing Circuit Switched voice services in the discontinuous transmission (DTX) state, because they are not transmitting data. Hence, the transmit power of these UEs is wasted. To improve the power efficiency of UEs that are performing CS voice services, OLPC takes Bit Error Rate (BER) and Block Error Rate (BLER) into account when assessing radio channel quality for higher accuracy and adjusts the target SIR of each voice frame more quickly. In addition, to improve the efficiency of transmit power of UEs, the DTX Power Control algorithm is used for CS voice services of UEs in the DTX state. While ensuring the uplink dedicated physical control channel (DPCCH) quality, this algorithm quickly decreases the target SIR to reduce the transmit power of UEs performing CS voice services.   This algorithm provides optimized OLPC, which apply only to the Uplink CS voice services; the optimized OLPC function consists of the OLPC algorithm based on BLER and BER and the DTX Power Control algorithm. The OLPC algorithm based on BLER is optimized by introducing BER for radio channel quality estimation, which facilitates accurate Power Control of UEs. The DTX Power Control algorithm quickly decreases the target SIR when no voice data is transmitted by UEs performing CS voice services in the DTX state to save transmit power of UEs. This would improve the mean opinion score (MOS) of narrowband voice and broadband voice services by about 0.05 to 0.1.   Figure 1:  Principle of the Normal Outer Loop Power Control for CS Voice Services   where the Node B reports the Cyclic Redundancy Check (CRC) and Quality Estimate (QE) results to the Radio Controller. When the CRC result is 0, correct voice frames are received by the Node B. When the CRC result is 1, incorrect voice frames are received by the Node B. The QE result is the quantized BER. According to section 6.2.4.5 "Quality Estimate" in 3GPP TS25.427 and section 9.2.9.2 "Transport channel BER measurement report mapping" in 3GPP TS25.133, the quantization formula of QE is    ()  ()   BER ranges from 0 to 1, and therefore the QE result ranges from 0 to 255.  Optimized Outer-Loop Power Control Based on BLER and BER The Outer-Loop Power Control based on BLER and BER uses both the BLER-based Outer-Loop Power Control algorithm and BER-based Outer-Loop Power Control algorithm. Figure 2 below illustrates the principle of Outer-Loop Power Control.    ISSN: 2617-6513 (Online), ISSN: 2409-0263 (Print) 271 Figure 2:  BLER-based Outer Loop Power Control   The BLER-based Outer-Loop Power Control algorithm calculates the BLER measurement value according to the CRC result. It then determines whether to adjust the QE target value (QE target) by comparing the BLER measurement value (BLER meas) with the BLER target value (BLER target).           ()   BER-based Outer Loop Power Control The BER-based Outer Loop Power Control function determines whether to increase or decrease the SIR target value (SIR target) by comparing the QE (BER quantized value) reported by the Node B with the QE target after adjustment. For the first frame, the SIR target before adjustment is the initial SIR target.  DTX Power Control When performing a voice service in the DTX state, a UE transmits only control information (such as pilot information and Transmit Power Control (TPC) command and does not transmit data on the Uplink DPCCH. DTX Power Control appropriately reduces the target SIR while ensuring the DPCCH quality, thereby reducing transmits power of UEs.  Optimized Multipath Searching The multipath searching algorithm calculates the accumulated power of all signals in a timeslot based on pilot information and the accumulated power is used to determine the multipath status. However, when the SIR is low, the signals in some paths are so weak that the accumulated power of these signals may be surpassed by noise and the signals fail to be detected. The optimized multipath searching algorithm accumulates all pilots of multiple timeslots for assessing the multipath signal quality. In this way, the impact of noise on signal quality is reduced and the performance of searching for weak signals in low-SIR scenarios is enhanced, thereby improving the accuracy of ILPC.  Optimized SIR Estimation The SIR estimation algorithm estimates the SIR based on all pilots of a timeslot. However, the pilot information of a single timeslot is insufficient for accurate SIR estimation. The optimized SIR estimation algorithm uses all information of the previous timeslot and pilot information of the current timeslot to obtain the average SIR of the two timeslots, which facilitates accurate ILPC. The CS Precise Power Control feature is a substitute for the conventional Power Control feature. On the Network Controller, when it is permitted, the conventional Power Control based on BLER no longer has effect; else, the conventional Power Control based on BLER takes effect.    Islamic University Multidisciplinary Journal Vol. 6 Issue 2, June, 2019 272 Results and Discussion Figure 3:  Uplink Bler AMR and SIR Target   In figure 3 above, the rate of duration during which Uplink Bler exceeds target and SIR target reaches maximum values has reduced significantly after optimized Outer Loop Power Control algorithm was activated. Mean daily average for rate of duration during which ULBLER exceed target was 2.08% while the duration when SIR target reaches maximum value reduced by 0.218%   Figure 4:  Uplink Bler AMR N Band Uplink Bler AMR WB.   From figure 4 above, it is observed that the ULBLER on both NB and WB samples improved by 0.115% and 0.474% respectively.   Table 1:  Normal and Optimized Outer Loop Power Control vs ULBLER (%)   KPI   Normal Outer Loop Power Control   Optimized Outer Loop Power Control   Delta (%)   Day1   Day2   Day3   Day4   Day1   Day2   Day3   Day4   ULBler.AMR (%)   0.280 0.279 0.283 0.278 0.206 0.151 0.155 0.149 - 0.115 ↑  ULBler.AMRWB (%)   0.785 0.774 0.777 0.795 0.442 0.255 0.282 0.256 - 0.474 ↑  ULBLer.Out.AMR (%)   4.268 4.264 4.276 4.257 2.985 1.888 1.949 1.921 - 2.08 ↑  ULSirTarget.Out.AMR (%)   0.647 0.637 0.636 0.654 0.543 0.381 0.403 0.373 - 0.218 ↑   00.20.40.60.811.21.41.601234567    1   2  :   0   0  :   0   0   A   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M   4  :   0   0  :   0   0   A   M   1   1  :   0   0  :   0   0   A   M   6  :   0   0  :   0   0   P   M   1  :   0   0  :   0   0   A   M   8  :   0   0  :   0   0   A   M   3  :   0   0  :   0   0   P   M   1   0  :   0   0  :   0   0   P   M   5  :   0   0  :   0   0   A   M   1   2  :   0   0  :   0   0   P   M   7  :   0   0  :   0   0   P   M   2  :   0   0  :   0   0   A   M   9  :   0   0  :   0   0   A   M   4  :   0   0  :   0   0   P   M   1   1  :   0   0  :   0   0   P   M   6  :   0   0  :   0   0   A   M   1  :   0   0  :   0   0   P   M   8  :   0   0  :   0   0   P   M   3  :   0   0  :   0   0   A   M   1   0  :   0   0  :   0   0   A   M   5  :   0   0  :   0   0   P   M   1   2  :   0   0  :   0   0   A   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M   4  :   0   0  :   0   0   A   M   1   1  :   0   0  :   0   0   A   M   6  :   0   0  :   0   0   P   M   1  :   0   0  :   0   0   A   M   9  :   0   0  :   0   0   A   M   4  :   0   0  :   0   0   P   M   1   1  :   0   0  :   0   0   P   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M 3/16/2017 3/17/2017 3/18/2017 3/19/2017 3/20/2017 3/21/2017 3/22/2017 3/23/2017 3/24/2017 3/25/20173/26/2017    U   L   S   i   r   T   a   r   g   e   t   U   p    l   i   n    k   B   L   E   R  VS.ULBLer.Out.AMR (%) VS.ULSirTarget.Out.AMR (%) 00.20.40.60.811.21.400.050.10.150.20.250.30.350.40.45    1   2  :   0   0  :   0   0   A   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M   4  :   0   0  :   0   0   A   M   1   1  :   0   0  :   0   0   A   M   6  :   0   0  :   0   0   P   M   1  :   0   0  :   0   0   A   M   8  :   0   0  :   0   0   A   M   3  :   0   0  :   0   0   P   M   1   0  :   0   0  :   0   0   P   M   5  :   0   0  :   0   0   A   M   1   2  :   0   0  :   0   0   P   M   7  :   0   0  :   0   0   P   M   2  :   0   0  :   0   0   A   M   9  :   0   0  :   0   0   A   M   4  :   0   0  :   0   0   P   M   1   1  :   0   0  :   0   0   P   M   6  :   0   0  :   0   0   A   M   1  :   0   0  :   0   0   P   M   8  :   0   0  :   0   0   P   M   3  :   0   0  :   0   0   A   M   1   0  :   0   0  :   0   0   A   M   5  :   0   0  :   0   0   P   M   1   2  :   0   0  :   0   0   A   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M   4  :   0   0  :   0   0   A   M   1   1  :   0   0  :   0   0   A   M   6  :   0   0  :   0   0   P   M   1  :   0   0  :   0   0   A   M   9  :   0   0  :   0   0   A   M   4  :   0   0  :   0   0   P   M   1   1  :   0   0  :   0   0   P   M   7  :   0   0  :   0   0   A   M   2  :   0   0  :   0   0   P   M   9  :   0   0  :   0   0   P   M 3/16/2017 3/17/2017 3/18/2017 3/19/2017 3/20/2017 3/21/2017 3/22/2017 3/23/2017 3/24/2017 3/25/20173/26/2017    W   i    d   e   B   a   n    d   A   M   R   N   a   r   r   o   w   B   a   n    d   A   M   R  VS.ULBler.AMR (%) VS.ULBler.AMRWB (%)
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