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Most mature 3G network system is the WCDMA developed by the 3GPP project team. WCDMA network structure, can refer to Figure 12.1, which has several characteristics.
1. Reverse-compatible Gsm/grps network.
The base station subsystem (BSS) of the original GSM network remains unchanged and can be interconnected with the transformed core network via the original a protocol stack and the GB protocol stack.
2. The core network maintains the network structure of the original Gsm/grps/edge network HLR,AUC,EIR,VLR,MSC,SGSN,GGSN and so on.
The main change is to split the original MSC into MSC (Mobile switching Center) and MGW (Media Gateway). After the split MSc, is still responsible for establishing the connection between the two sides of the circuit, and the two sides in the mobile process, constantly switch the base station, maintain the voice of continuous. However, the WCDMA network to switch the task of the circuit to the MGW dedicated division, not only to improve the efficiency of the system, but also facilitate the maintenance of the system [1, pp134].
3. Add a community service broadcast function. The
Community Service Broadcast Centre (cell Broadcast Center) is responsible for broadcasting all kinds of messages, such as weather, stocks, real-time traffic information, etc. to the cell phone.
4. The original base station subsystem (BSS) of the GSM network is no longer used in the UMTS/WCDMA system, and is replaced by the UMTS terrestrial Wireless access network (UTRAN,UMTS terrestrial Radio access networks). In
utran, the base station Node B is responsible for wireless contact with the phone, which functions like the BTS in the GSM BSS subsystem. The functions of the RNC (Radio Network Controller) in Utran are similar to the functions of the base station controller (BSC) in the base station subsystem (BSS) in the GSM network. However, because the multi-access mode of GSM is time division multiple address (TDMA), and the multiple access mode of UMTS/WCDMA is CDMA, the technology used by base station and base station supervision is very different. Therefore, the original GSM BTS and BSC, it is difficult to use in WCDMA, had to reinvent the Node B and the RNC to replace them [1, pp198].
Figure 12.1 3g/umts/wcdma Release 4 Network Architecture .
In the UMTS/WCDMA network specification, not only node B,RNC,MSC,MGW,SGSN,GGSN, and CBC and so on network components, but also uu,iub,iur,iu-cs,iu-ps, and IU-BC and so on the protocol stack. The so-called protocol stack, which is a series of protocols used when transferring information between network components, is stacked into a stack structure, so called the protocol stack (Protocol stack), as shown in Figure 12.2.
1. The UU protocol stack is responsible for transmitting information wirelessly between the mobile phone and the base station Node B. Therefore, the UU wireless protocol stack is directly related to the technical realization of the BP part of the smartphone.
2. Utran in the Base station node B, with the wireless network Controller (RNC), collectively known as the Wireless network system (RNS). The protocol stacks between them are iub and iur, in Figure 12.2, not detailing Iub and iur, but merging Node B with the RNC into RNs, which focuses on RNs and the outside world, the protocol stack between the mobile phone and the core network.
3. The RNC uses the IU-CS protocol stack when processing voice services. However, the use of Iu-cs is controlled by the level of control Plane and user Plane.
The RNC uses the Iu-cs control plane (Iu-cs control) to contact MSC when establishing a circuit that contacts both sides of the call. After the circuit is switched on, the RNC uses the Iu-cs user plane (Iu-cs Bearer) to communicate with MGW in the process of transmitting the voice signals of both parties, see figure 12.1.
4. The RNC uses the IU-PS protocol stack when processing data services, and is always only associated with SGSN. However, the contact method is also divided into control level and user level. Figure 12.2 Describes the various protocol stacks that transmit signaling and data entities in the process of processing data services.
Although they belong to the IU-PS protocol stack, the specific protocols used at different levels are not the same for the control plane and user level. Figure 12.2 The upper part describes the protocol stack on the control plane, which is responsible for establishing the data channel, while the second half of the figures 12.2 describes the user level protocol stack, which is responsible for transmitting the data entity.
5. The BP part of the smartphone needs to implement all the protocols contained in the left block diagram of the UU protocol stack.
In the case of data Services, the BP part of the smartphone is to achieve the most left-hand block diagram of the upper half of Figure 12.2, which depicts various protocols related to the handset (UE), namely the various protocols involved in the Rf-mac-rlc-rrc-gmm/sm/sms modules, To complete the task of establishing a data channel, which is the work of the control plane. It is also necessary to achieve the leftmost block diagram of Figure 12.2, which describes the various protocols associated with the handset (UE), the various protocols involved in the RF-MAC-RLC-PDCP-IP/PPP, and the related applications (applications), To transfer data entities, which is a user-level effort.
Figure 12.2 Umts/wcdma GRPs Protocol Stacks, Release 99.
[1, Figure 6.24, pp 237, and figure 6.25, pp238]
Next, we analyze the BP part of the smartphone, the work that the control plane needs to deal with when establishing the data transmission channel, and the work that the user level needs to handle when transferring the entity. In Figure 12.2, the upper-left block diagram of the top half, the protocol associated with the handset (UE), which is the protocol involved in the Rf-mac-rlc-rrc-gmm/sm/sms five modules, interacts with each other. Also included is the bottom half of the leftmost block diagram, the protocol associated with the handset (UE), which is rf-mac-rlc-pdcp-ip/ppp-application, the protocols involved in the six modules interacting with each other.
Figure 12.3 Depicts some of the protocols contained in these modules, as well as the interrelationships [2,3].
1. Each module can be vertically divided into layers (layer), each module only with the upper and lower layer of the corresponding module, but not with the other modules in the same layer contact.
bottom up, the physical layer, respectively.rf/phy(layer 1), Link layer(Layer 2), includingMAC/RLC/PDCP/BMCeach module, and the network layer(Layer 3), including RRC and network Control/amr voice/cs data/ps Data modules.
At the same time, the bottom-up whole system is divided into Access layer (access Stratum,as) and non-access layer (non-access Stratum,nas). The module of the non-access layer is responsible for contacting the core network, such as the network control module, which is responsible for telephone call and call CONTROL,CC, and keeps the call continuous (Mobility management,mm) when the cell phone switches the base station. and ensure the normal transmission of packets (GPRS Mobility management,gmm) and so on.
The module of the access layer is responsible for the local connection within the wireless network system (RNS), including the local connection between the mobile phone (UE) and the base station (Node B), the base station and the base station, and the base station controller (RNC). In addition, the connection between the base station controller (RNC) and the core network IU-CS/IU-PS/IU-BC protocol stack is included. The access layer provides basic services for non-access layers .
2. The protocol stack is divided into control Plane and user Plane.
Figure 12.2 is divided into the upper and lower sections, the upper part describes the control plane, and the lower half describes the user level. Figure 12.3 puts the control plane on the left side of the graph, placing the user level on the right side of the graph.
taking the non-access layer as an example, the control plane includes network control, which is responsible for call control (CC), Mobile call Management (MM), and Packet Management (GMM). The user level is responsible for the transmission of voice and packet entities, corresponding to three functional modules, respectively, is responsible forCircuit SwitchingDataTransmission Module (Circuit switched Data,cs Data), the packageExchanging DataTransmission Module (Packet switched Data,ps Data), andresponsible for voice delivery.Adaptive Multi-speed voice encoder (AMR voice).
3. Wireless interface and channels (channel)
For mobile phones (UE), the physical layer (layer 1) and the link layer (Layer 2) are responsible for the use of wireless bands to transmit data, the two-layer protocol data encoding is called Channel , including the following three categories,
1. Physical Channel(RF), Dpch,p-ccpch,prach, S-ccpch,aich, PICH.
2. Transport Channel (Phy-mac, defining the way data is transmitted ), DCH, PCH, Bch,rach,fach.
3. Logical Channel (MAC-RLC, which defines the type of data transmitted ), Dcch,ccch,bccch,dtch.
the content of the network layer (layer 3), mainly the Wireless resource Control (RRC) protocol, is responsible for controlling the allocation of wireless resources and sending related control signaling.
Figure 12.3 Umts/wcdma Uu Protocol Stacks and its internal interaction .
Understanding the various protocols contained in the UU protocol stack, as shown in Figure 12.2, and the interaction between them, as shown in Figure 12.3, it is not difficult to understand the system architecture of the BP part of the smartphone. Figure 12.4 is a system architecture diagram of the BP part of a smartphone that is used in 4G LTE networks and produced by the UK 4M Wireless Ltd. But this BP part of the system architecture, and 3G mobile phone BP part, structurally similar.
Although structurally similar, but corresponding to different mobile networks, such as WCDMA and TD-SCDMA, each module implementation details are not exactly the same, resulting in the corresponding hardware may not be common. This is the so-called "dual-mode dual-standby" mobile phone existence significance.
Specifically, due to the 3G data transmission speed of 2M to 7.5MB/S (HSPA), real-time requirements are much higher than 2G, so the BP part of 3G usually use a number of DSP hardware and so on dedicated processors, to deal with protocol data encoding and decoding, and not the method of using software. The use of hardware is guaranteed speed, but for different communication protocols, such as 2G Gsm/grps, and 3G Wcdma/hspa, there is a need for different hardware mates.
Different countries and regions also use different frequency bands, RF parts are also different. 2G mobile phone as long as support Gsm/gprs/edge 850/1900 and 900/1800 can be called the World Mobile phone (except Japan and Korea outside). 3G of the world's mobile phones, generally need to support 2G of all protocols and bands, plus 3G of 2100/850/1900 ( covering Japan and South Korea). Compared to MTK function phones, these predecessors are mostly more complex than the BP portion of a gsm/gprs,3g phone that supports only 2 bands. If the MTK's BP complexity is likened to 8086,the complexity of 3G mobile phone BP may be equivalent to Core2 Duo.
all of this makes the BP part of the 3G smartphone very difficult to develop. in the 2G era, Ti+nokia's invincible combination, once occupied most of the market share, became the market overlord. However, due to the rise of MTK, as well as the delay of 3G chip shipments, so ti gradually lost the baseband chip market advantage. As for other baseband chip manufacturers in the 2G era, when NXP was acquired to survive, Broadcomm tried to compete for the market at a low price, but almost nothing. Marvell's Tavor won RIM's order, but the subsequent weakness. now only Qualcomm maneuvers, with AP+BP Soc chip, firmly occupy the 3G single-chip market. At the same time, Qualcomm uses the low-end 3G BP chip, and Infineon competes for the BP special chip market.
Because the BP part is responsible for processing calls, real-time requirements are very high, so the BP part of the operating system must be a real-time operating system (RTOS), such as Vxworks,nucleus, and THREADX and so on. The real-time operating system is responsible for the task scheduling of all functional modules for each layer, as shown in Figure 12.4, the rightmost vertical yellow box.
Figure 12.4 3G SmartPhone BP architecture .
To summarize,the BP part of a smartphone is actually a modem. The difference between it and the functional phone is only that, in addition to the Sim/usim this peripheral is retained, other peripherals and human interface are removed, instead of the AP side of the control interface, similar to the RMI system, refer to the 7th chapter of this series, MTK mobile phone software system.
The BP part of the smartphone is divided into several vertical distribution layers, which correspond to different network transmission protocols. At the same time, the level is divided into control and user two planes, respectively, responsible for the management of information channels, and responsible for the delivery of information entities.
The BP part of the smartphone has an independentReal Timeoperating system,for each layer of each planeall of the included function modules, providing the most basic operating system kernel services, such as task scheduling, CPU and memory management, etc.
the BP part structure of the smartphone is quite complex, which corresponds to different types of networks, the band segmentation in different regions, the software and hardware are difficult to be common.
 3G Wireless Network, 2 ' nd Edition. Isbn-13:978-0-07-226344-2.
 WCDMA Radio Access Network Concepts.
 Wireless protocols.
 WCDMA Radio Access Network Architecture.
 WCDMA physical, Transport and Logical Channels.
 BP Architecture by 4M Wireless LTD.
On cottage phone and Android "12" 3G era smartphone BP part
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