GSM Dynamic PBT Solution White Paper
Huawei Technologies Co., Ltd. All rights reserved.
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GSM Dynamic PBT White Paper
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GSM Dynamic PBT Solution White Paper 1
Introduction to the Coverage Enhanced Technology
1.1 Latest Coverage Enhanced Technology With the development of GSM, operators are more and more focusing on the construction and operation cost of a network. With the competition more toughly, operators require the quickly setup of a network. In order to save the total cost of ownership (TCO), quickly set up a network by reducing the number of sites and win the competition, the leading GSM operators have adopted the latest coverage enhanced technology and the strategy that the wireless technology of 3G is used in 2G. In 2006, Huawei launched the leading double density BTS in the GSM field. Based on the double density transceiver (TRX), Huawei also launches the technologies such as power boost technology (PBT), transmit diversity (TD) and 4-way receive diversity (4WRD). The PBT emerges and enlarges the double-transceiver unit (DTRU) power amplifier unit (DPAU) of two TRXs. Thus the output power of TRXs can reach from 60W to 100W and the downlink gain can reach round 3dB. Through two single polarization antennas or a set of dual-polarization antenna, along with the transceiver with two TRXs, the TD transmits the same downlink signals and obtains the downlink gain ranging from 3dB to 5dB. Through two single polarization antennas or a set of dual-polarization antenna, along with the transceiver with two TRXs, the 4WRD operates the four diversity combination and obtains the uplink gain ranging from 3dB to 5dB. If operators adopt Huawei ICC technology, the uplink gain can be increased. The static sensitivity of Huawei GSM TRXs in the DTRU reaches -112.5dBm, which plays a leading role. Therefore, together with the 4WRD and ICC, the uplink sensitivity can reach -118dBm.
1.2 Market Value of the PBT In the industry, all the PBT, TD and 4WRD are realized by two TRXs combined into one TRX. Thus the coverage is enhanced and the number of sites is reduced, which is the coverage mode in the first stage of setting up a network. With the development of the network, the capacity becomes a bottleneck. To obtain large capacity, operators can convert the coverage mode into the capacity mode and delete the configurations of PBT, TD and 4WRD. To meet the requirement of coverage, operators can add sites. What's more, operators can adopt the strategy that the coverage enhanced technology is used for partly TRXs and common configurations for other TRXs in a same cell. Operators can also adopt the concentric cell strategy to balance the capacity and coverage. For the coverage enhanced technologies such as PBT, TD and 4WRD used in the actual network, if the coverage mode is converted into the capacity mode for one site, operators need not adjust the hardware but modify the configurations through the remote console. There is no special requirement for terminals. Therefore, it is easy to realize these technologies. Operators can save the maintenance personnel, quickly set up a network and win the terminal user market. 2009-3-26
Huawei Technologies Proprietary
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GSM Dynamic PBT White Paper
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The downlink coverage enhanced technologies, such as PBT and TD, can be used together with the DFCU/DFCB to meet the site requirements. In the situation that the coverage is limited, operators can use the TD to obtain the downlink gain in the S1/1/1 and S2/2/2; while use the TD or PBT in the S3/3/3 and S4/4/4. However, in many cases, the PBT is more suitable, because the TD requires many antenna feeders. For the configuration higher than S4/4/4, operators can use the DFCU/DFCB. The DFCU/DFCB can be flexibly configured and expanded with TRX capacity. The DFCU/DFCB has small insert loss. In the S6/6/6, the insert loss is only 3dB. The common insert loss is more than 6dB.
1.3 Evolvement of the PBT The PBT is required for quickly setting up a network and saving the TCO for operators. Similar to the technology of other manufacturers, the PBT can work based on only the unit of TRX when used in a TRX. In actual situations, an unexpected high traffic may be present. Therefore, if the PBT can balance the coverage and capacity (traffic), its market value will be improved.
For the investment of operators: The user distribution of a cell can be regarded as an average distribution. According to the network planning and the statistics on the call quality, there are 20% users of a cell who receive poor signals. That is, 80% users can make calls of strong signals. For the 80% users, the signals need not be enhanced. Operators need to consider how to enhance the signals for the 20% users. The PBT and TD are not suitable in the situation, because that 50% capacity is used for the 20% users is wasteful to the investment.
Poor Covered Area
Good Covered Area
In general, the channel usage does not exceed 80% and 20% of the time slot is in idle except in the high traffic time. Therefore, operators expect to full use the 20% idle channel. 2009-3-26
Huawei Technologies Proprietary
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GSM Dynamic PBT White Paper
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As required, the PBT is evolved flexibly and intelligently. It is Huawei that launches the dynamic PBT.
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Dynamic PBT
2.1 Introduction to the Dynamic PBT The dynamic PBT means that some pairs of channels within the DTRU module can work under PBT, instead of all of the channels. Compared with the current PBT, the dynamic PBT is more specific. The user in a call occupies a dedicated timeslot. The call quality can be monitored through the measurement report. When the call signal is lower than the threshold, the dynamic PBT is started to distribute the same timeslot of an adjacent transceiver to the user. The signals that the two timeslots send are the same, as well as the phases. After the two timeslots are combined, the signal can be enhanced by 6dB. Thus the call quality is improved. When the call signal is higher than the threshold, the dynamic PBT is canceled to release the adjacent channel. When the adjacent channel is occupied, the handover between cells is started. The call is switched to an idle channel, and then the adjacent channel that becomes idle is used for the dynamic PBT. During the handover, the call is not dropped because the receiving signal is strong. As shown in the following figure, the timeslots of two TRXs are used for different users. When the receiving signal is strong, the PBT mode is not needed. Timeslot
Capacity
0 1 2 3 4 5 6 7
Good Covered
Poor Covered
Out of Coverage
Quality of Signal
2009-3-26
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GSM Dynamic PBT White Paper
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When the call of a user who is in an area with poor signals is in poor quality, the dynamic PBT is started to combine the signals of two adjacent timeslots. If the adjacent timeslot of the user is occupied, switch the signal of the timeslot to another timeslot. After the combination, the transmitting power is improved; the Rx level of the terminal and the voice quality is enhanced, as shown in the following figure:
Timeslot
Capacity
0 1 2 3 4 5 6 7
Good Covered
Poor Covered
Out of Coverage Quality of Signal
Dynamic PBT has no special requirement on HW. That is, through SW upgrade and purchasing the function License, customers can deploy this feature in the network. For example, a subscriber is parking his car in the basement. Although he is within the coverage radius of the site, the signal is weak. If Dynamic PBT used, the system can assign two channels to this subscriber and improve the signal quality. Dynamic PBT can also deployed together with Half Rate to expand the capacity.
2.2 Market Value of the Dynamic PBT 2.2.1 Dynamically Balancing the Capacity and Coverage Huawei launches the dynamic PBT using idle timeslot. For the area with poor signals, such as the edge of a cell, indoor and in-vehicle area, the signal is enhanced. The network resource is not wasted and the capacity is not reduced. The capacity and coverage are kept in good balance. 2.2.2 Improving the Performance of the CO-BCCH Concentric Cell At present, many operators obtaining GSM900 band use the DCS1800 band to absorb capacity. Because the combination solution and multiple frequency bands are used in many networks, especially in densely populated areas, as well as the capacity is limited, the concentric cell technology is widely used. However, this technology has a fatal disadvantage. That is the handover between the overlaid subcell and 2009-3-26
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GSM Dynamic PBT White Paper
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underlaid subcell and the assignment are blind. TA is used for reference, which is caused by the GSM itself. When the assignment is operated from the underlaid subcell to the overlaid subcell, the dynamic PBT can be adopted to temporarily widen the coverage of the overlaid subcell and make the user occupying the overlaid subcell channel. Then operators can judge the signal according to the measurement report. If the signal reaches the threshold, the dynamic PBT is cancelled and a channel is released. If the signal does not reach the threshold, two channels are used or handover is operated from the overlaid subcell to the underlaid subcell. For the latter, the handover is according to the occupation of the overlaid subcell channel. This solution can improve the performance of the CO-BCCH concentric cell. 2.2.3 Realizing the Same Coverage for the 8PSK and GMSK In general, the maximum transmitting power in GMSK modulation mode is more than the maximum transmitting power in 8PSK modulation mode. The EGPRS requires good-quality signal, while the users using EDGE services are very few. If operators plan the network according to the requirements of EDGE services, the cost is very high. Through the dynamic PBT, operators can widen the EDGE coverage to have the same coverage as the GMSK. Thus the users remote from the BTS can use the EDGE services. 2.2.4 Improving the Data Service Quality At present, the data service mainly covers surfing and downloading. Improving the downlink network quality can speed up the download and increase the satisfactory of users. In general, high-end users use more data services. The dynamic PBT can ensure the loyalty of high-end users and the ARPU. 2.2.5 Protecting the Investment of Operators Operators expect to full use the invested equipment. In general, the 20% channel is in idle status. When the channel usage exceeds 80%, operators need to consider the capacity expansion. Thus the 20% idle channel is wasteful to the investment. It is very important for operators to full use the idle resource to provide better services. The most efficient way is to full use the current resource. 2.2.6 Reducing Power Consumption In general, if the downlink transmitting power is 60W and the combination loss is 3dB, the output of the antenna connector is 30W. The other 30W is dissipated as heat. When adopting the dynamic PBT, operators prepare only two sets of 15W output power to obtain the 30W antenna connector. That is, 30W consumption is reduced. Thus the power consumption of the system is obviously reduced.
3
Conclusion The dynamic PBT is mainly used in the S3/3/3 and its higher configuration. The BCCH TRX which requires the stable power output cannot adopt this technology. 2009-3-26
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GSM Dynamic PBT White Paper
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The dynamic PBT is more applicable to the small-capacity situation, for example, a 4-TRX cell. The dynamic PBT enriches Huawei coverage enhanced solution. It complements other technologies, such as the PBT, TD and filter combiner unit, to meet different coverage requirements. The complement can protect the operators' investment to most extent by full using idle timeslots but not reducing the network capacity.
Copyright©2007 Huawei Technologies Co., Ltd. All Rights Reserved. The information contained in this document is for reference purpose only, and is subject to change or withdrawal according to specific customer requirements and conditions.
2009-3-26
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