Optimization Analysis of PHS Network for DSP Dual Mode Mobile Phone

In this article, we mainly discuss the optimization of the PHS network (PHS, P network) and the impact of dual-mode mobile phones on the PHS network. Wireless network optimization includes optimization of terminals, base stations and core networks. GSM (G network) and 3G (C network, including 2G IS-95) have better network optimization solutions.
At present, domestic GSM, PHS, CDMA and other multi-network coexist, in order to make full use of these network resources, multi-mode mobile phones came into being. Built on zero-frequency (RF) technology and DSP digital baseband processor, the multi-mode mobile phone provides cost-effective power and reduces wireless communication caused by overloading a single network. Failure probability. Moreover, the PHS dual-mode mobile phone can realize the collaborative optimization of the PHS network at a lower cost by using DSP technology, and improve the instantaneous load capacity and service quality of PHS. PHS's network optimization is not long, but it is under tremendous pressure.
The problem of PHS network optimization PHS has the advantages of low power consumption, low radiation, low cost, etc., and has won quite a lot of favor in the low-end market. PHS also has some defects, low transmission power, severe scattering, and fast signal fading. In response to these shortcomings, the PHS network uses microcellular technology, and the microcell technology has an added benefit that it can theoretically carry more users. However, microcellular technology needs to set up more base stations, especially in urban areas with complex environments and high traffic. There are three factors affecting PHS service quality. Terminals (mobile phones), base stations and core networks can be regarded as part of network optimization. Terminals and base stations are optimized for wireless parts, and core networks are wired parts. The optimization of the wireless part can improve the service quality of the system to achieve a multiplier effect. Different from GSM network optimization (the base station and the core network in the GSM network are almost responsible for all optimization tasks), the PHS standard does not specify the responsibility of the base station for network optimization, so the optimization of the wireless part can only start from the base station, such as clearing the blind zone, Reduce adjacent channel interference, optimize antenna elevation angle, etc. Some can be responsible for the mobile phone, such as predicting, analyzing network phase characteristics, initiating handover, changing transmit power, increasing C/I ratio, and nonlinear compensation for transmission and reception.

Although the optimization of the wireless part is crucial and effective, it is incompatible with the development strategy of PHS, whether it is from the terminal or the base station. From the perspective of the base station, the number of base stations required by the PHS network is large. According to the power calculation and regardless of the reflection factor, the number of PHS base stations is more than 25 times larger than the number of GSM base stations to cover the same area. Because of the lack of good planning in the early construction process of the PHS network, and simply adopting technologies such as increasing coverage, eliminating blind spots and multi-layer coverage, operators' optimization of base stations is inevitably hindered by cost and capability: the cost problem is reflected in the huge The number of base stations for testing, analyzing, updating parameters, and even mobile base stations is complicated and costly. The capability problem is reflected in the randomness of the base station planning and the statistical characteristics of the PHS modulation method. The conventional road test technology for GSM networks. And the analytical model is far from meeting the needs of PHS. From the mobile phone side, PHS continued to reduce costs, although thanks to advances in technology, the performance of new mobile phones is not lower than that of old mobile phones, but it also lost the opportunity to improve performance to optimize the auxiliary network.
Optimization of the core network is another way, but the optimization of the core network is to balance the access load to improve the success rate of access and handover. This requires knowledge of base station coverage parameters such as base station boundaries, overlapping areas, and cell transient fading characteristics. The acquisition of these parameters is very difficult. For example, the PHS has no clear base station boundary and the fading is fast, which makes the drive test data unreliable. Therefore, relying solely on core network optimization is impossible.
The impact of dual-mode phones on service quality Wireless communication users can choose between networks and mobile phones. Taking PHS as an example, we do not consider mobile phone factors, we study the quality of service (QoS), tariffs / costs and user interaction.
First, the number of users has a great relationship with QoS, and QoS is related to the cost of operating inputs. The inflection point of N1(c) in Figure 1 is due to technical limitations in PHS networks, and excessive investment will cause QoS to fall. The intersection of the N1 and N2 curves indicates the number of relatively stable users the network has after the market has been more stable. All operators hope that this intersection will appear in the profit area.
The previous analysis curve for the network can be used for dual-mode phones. The dual-mode mobile phone can support two networks at the same time. If the air interface difference between the UA uU layer and the PHS is neglected, only the connection between the terminal and the core network is considered, and the result is equivalent to increasing the coverage of the wireless network. Its one-time access success rate (for both networks) is Pg+(1-Pg)Pp (Pg, Pp is the individual instantaneous turn-on success rate of each network). There is a similar improvement in the success rate of switching. It can be said that dual-mode mobile phones bring about an improvement in service quality. This has little effect on GSM, but the impact on PHS is huge, greatly expanding the roaming ability of PHS users. In the case that the operating cost does not increase, the dual-mode user is free to trade off the tariff and the quality of service, causing the intersection of the N1 and N2 curves to move to the right. As we will see below, dual-mode phones using DSP processors can do more than just these, and even improve the quality of PHS network services.

Structure and extension of the dual-mode phone We understand the construction of the dual-mode phone in a four-layer structure. From top to bottom, the single-mode mobile phone is the application layer (MMI), the transport layer, the network layer (L3), the data link layer (L2), and the physical layer (L1). In order to cooperate with the two Uu interfaces and the physical layer, the dual-mode mobile phone cooperates. Need to increase the media aggregation layer (MAC).
The earliest dual-mode mobile phone protocol stack architecture, which is relatively simple, bundles two target modules on L1. The PHS and GSM RF and digital baseband are respectively implemented by different chips and processors. To reduce the cost, the baseband processing chip is generally an ASIC, and the application layer including the MMI above L2 is completed by a control processor, generally an ARM chip. Such an architecture bundles the P-network and the G-network wireless modem (Modem) under the link layer, which is more synergistic than simply bundling two mobile phones. This architecture has several drawbacks: 1. Although ASIC cost and power consumption are low, because there are two sets of wireless modems integrated, there is not much advantage in terms of cost and power consumption; 2. Digital baseband adopts ASIC, lacking Flexibility, and this flexibility will play a huge role in optimizing the performance in the solution of Figure 2b; 3. Similar to Wi-Fi, two sets of RF and even antennas bring non-negligible interference, and the board Wiring is also complicated.
Another more advanced dual-mode solution. It uses only one RF chip to perform the demodulation of GSM and PHS. Therefore, the RF chip is required to lock the PHS and GSM frequency points, and can jump from one frequency point to another in a short time. Its digital baseband is also done by one chip, because the difference between the two decoding schemes is large, and it is suitable to use DSP chip to complete. In order to manage radio resources, arbitration may occur, and a unified interface is provided to the upper layer. A media aggregation layer (MAC) is embedded in L1, and the MAC and L1 thereon are all completed by the MCU. Compared with scheme a, the latter has the advantages of less hardware chips, small size and low power consumption, and because the digital baseband is completed by the DSP chip, it has better flexibility. However, this solution also has some shortcomings: 1. In order to reduce cost and complexity, the RF chip adopts zero-IF technology, which will bring or deepen the unfavorable factors such as local oscillator leakage, adjacent band interference and high-order intermodulation; DSP costs and consumes more power than ASICs; 3. Shared wireless hardware resources can cause mutual exclusion conflicts.
Future dual-mode phones and even multi-mode phones will go a step further and rely on network support. Similar to IP technology, it divides the network layer into two layers, and the lower layer has routing capabilities to establish interconnection of heterogeneous networks. After the user presets the policy, the multi-mode mobile phone can dynamically jump between the GSM network and the PHS network during standby and talk, and even use asymmetric wireless channels for uplink and downlink without affecting the user's operation. This technology solves the problem of network coverage in disguise, and the chance of dropped calls is greatly reduced for GSM or PHS communication.
PHS Network Optimization Supported by DSP Dual-Mode Mobile Phones Before we have a general understanding of the architecture of DSP dual-mode mobile phones, we focus on its features and implications for network optimization in this section.
DSP dual-mode mobile phones use DSP chips to complete the digital baseband part, including signal synchronization, waveform shaping, channel equalization, channel and source codec. In the early GSM mobile phones, in order to improve the receiving performance, the DSP chip was also used, but it consumes a large amount of power and has a high cost. With the deepening of network optimization, the DSP core wireless MODEM has been abandoned without the use of ASIC or FPGA (at a relatively high level of application), the supply of ASIC is also monopolized by a few companies. The same is true for PHS. Dual-mode handsets give DSP architecture an opportunity because different modulation modes and protocol standards require different baseband processing structures. If done by an ASIC, the volume will increase, and both routing and power consumption are disadvantageous. Today's DSP chips are very small in size and power consumption, and dual-mode phones can be seen as higher-end requirements because the added cost of DSP is negligible. In terms of chip supply, TI's OMAP and ADSP's Hermes all use DSP+ARM architecture, which can be considered as a multi-mode smartphone in terms of cost, power consumption and volume.

DSP dual-mode mobile phones can do more than ASICs, because the domestic GSM network optimization has been perfect, so DSP applications have no substantial effect on GSM. However, PHS is different. As mentioned above, PHS network optimization is very difficult and can be summarized as follows: 1. The base station has no clear boundary; 2. Lack of frequency planning; 3. Faster fading. The first problem leads to the disorder of switching, the second problem causes the same frequency and adjacent channel interference, which leads to passive switching channels or base stations, and the third problem causes the critical user capacity of the cell to change faster. Another problem is that PHS switching does not have a reasonable strategy. In the past, neither the terminal nor the network can analyze the channel characteristics in real time, and since the PHS channel jitter is much higher than GSM, the result of the road test instrument is unreliable. This often manifests itself in urban areas with complex terrain, such as high-rise buildings. After the quality of service reaches a platform, it does not increase with the number of base stations, and may even deteriorate.
The PHS mobile phone with DSP architecture is far superior to the ASIC core mobile phone in terms of transceiver performance. The DSP can complete the analysis of the channel parameters, select corresponding pre-stored processing procedures for different statistical characteristics of the channel, and interact with the core network to analyze the location of the terminal and predict the reliability probability of the base station. The DSP can also perform nonlinear compensation for the transmission, which is not possible with the ASIC. The enhancement of transceiver performance improves the instantaneous user capacity, and the analysis of the channel provides a more reliable basis for handover. Taking the area covered by multiple base stations as an example, simply selecting the base station by power factor may select it because the small base station is large at the moment of measurement, and the fluctuation of the small base station is faster, which has a very good call quality for roaming users. Big injuries, especially in urban areas, where the number of users is at a critical point, which is fatal to the entire network. The real-time measurement of the channel parameters can actively initiate the handover and speed up the handover speed, which is beneficial to the optimization of the load distribution in the cell.