移动通信系统的研究

发布时间：2016-03-18 13:30

WLAN（无线局域网）接入网络对于提供一个宽带3G（第三代）蜂窝系统而言显示出了很强的潜力。与WLAN（无线局域网）相比，第三代网络提供无处不在的连接和在更广泛的服务区中更快的速度。无线局域网提供了易于兼容和高数据速率的有线互联网，但覆盖小面积。整合WLAN和3G网络提供高速无线的数据服务并且随时随地的连接。实现这些目标的关键问题是加速3G和WLAN技术的整合。集成点的偏好取决于一系列的因素与安全性，移动性支持，切换延时，认证，成本效益，会计和计费机制。这说明，我基本上描述了3G和无线局域网802.11服务这两种机制，移动通信中手机技术的革命，3G与WLAN融合。

随着无线技术的发展和移动设备的广泛应用，，许多新的移动应用正在兴起。无线技术取决于硬件和软件技术，使设备之间信息的传播不需要利用物理连接。

Abstract摘要

WLAN (Wireless LAN) access networks demonstrate a strong potential in offering a broadband complement to 3G (Third Generation) cellular systems. 3rd generation networks offer a omnipresent connectivity and wider service area with less speed data rates as compared to WLANs (Wireless Local Area Networks). WLAN networks provide the easy compatibility and high data rates to wired Internet, but cover minor areas. Integrating WLAN and3G networks provide high speed wireless data services and ubiquitous connectivity to the subscribers. The key concern involved in realizing these objectives is the expansion of integration of 3G and WLAN technologies. The preference of the integration point depends on a numeral of factors with security, mobility support, handoff latency, and authentication, cost-performance benefit, accounting and billing mechanisms. In this description, I essentially described about the introduction of two mechanisms 3G and Wireless LAN 802.11 services, generations in mobile communication, mobile phone technology revolution and integration of 3G and WLAN.

Introduction引言

With the development of wireless technology and extensive use of mobile devices, many new mobile applications are emerging. Wireless technology demotes to the hardware and software that allows the broadcasting of information between devices without utilizing physical connections. Understanding the dissimilar mechanisms that are available, their limits, and uses can benefit companies seeming at this technology as a possible option to develop overall efficiency and effectiveness. By increasing the useage of mobile technology there lot of changes occured in the mobile generation they are explained below.

Generations in Wireless Technology无线技术一代
There are several technologies within each categorization of generations, but the mechanisms are not essentially finite in these generations.

First Generation (1G)第一代（1G）
The 1st generation mobile refers to the mobile phones that were urbanized in the 1980s. First generation mobile communication hold analog cellular system and does not provide data services. It can only provide voice services to the mobile phones. 1st generation analog cellular phone system standard are NMT (Nordic Mobile Telephony), AMPS (Advanced Mobile Phone System), Total Access Communication System (TACS), Radicom 2000 and Radio Telephone Mobile Systems (RTMS).

SecondGeneration (2G)第二代（2G）
2G is a digital wireless telephone technology that utilizes circuit-switched services. GSM, TDMA and CDMA are the some protocols, which brought the mobile phone into the 2nd generation stage. The protocols of the 2nd generation mobile phone are digitalized broadcasted. Short Message Service (SMS) is also the services extra for the 2nd generation services. The 2nd generation was commenced to the market mostly in the early 1990s. Standards of 2G systems were Global System for Mobile communication (GSM), Personal Digital Cellular (PDC), Code Division Multiple Access (CDMA) and Digital AMPS (D-AMPS).

Second And a Half Generation (2.5G)第2.5代（2.5G）
It is in the same protocol, but offered services such as Wireless Application Protocol (WAP) and General Packet Radio Service (GPRS) allowing mobile phones to access on certain websites. Coloured screen with camera characteristic mobile phones were also commenced in this stage. A 2.5 GSM system contains one of the following Techniques to upgrade from GSM they are General Packet Radio Service (GPRS) and Enhanced Data rate for Global Evolution (EDGE).

Third Generation (3G)第三代（3G）
A complete new network protocol was commenced in the 21st century. It is also under UMTS and IMT-2000 standards. The 3rd generation protocol provides high speed connection to access through internet and video calls also.

Introduction to 3G Technologies:3G技术的介绍

The potential of 3G systems will maintain to steadily develop in the future because of the increasing traffic level of mobile function and the demands to offers progressively more cost well-organized mobile communication infrastructure. From a network perspective and radio access, it is estimated that the future expansion of mobile communications systems will be construct on and combine the technologies and systems already being urbanized and deployed, thereby defending the massive investment in mobile systems. This development will improve stability and encourage the expansion of an increasing number of services and functions. Academic and Industrial followers are functioning together on 3G Evolving Technologies (3GET).

What is 3G?

3G stands for third generation, is a communal expression for the new communication events, principles and campaign that will develop the quality of services and speed obtainable on the move. 3G obtain the form of handsets that can combine the functionality of a mobile phone with a personal organizer/PDA and a personal computer. 3G devices normally have superior transmission ability, both in conditions of capacity and speed, than their predecessors. The ITU describes 3G as a device that can broadcast and receive data at 144K bps or more. In real, 3G devices can broadcast data rate at up to 384Kbps, which is quicker than numerous home broadband connections. As a evaluation, GPRS is around 53.6Kpbs with theoretical maximum rate of up to 171.2Kbps and GSM is up to 14.4Kbps.

Working of 3G:
3G chops every call or communication into small packets of data, marking every one with a personage code to demonstrate to which connection it belongs. This is a much more proficient way of broadcasting data, permitting 3G networks to transfer better files like videos and pictures at much faster speeds.

3G Standards:
The 3G standards were created by the international Telecom Union (ITU). The purpose this technology is to offer global roaming in worldwide using 3G system. The standard of 3G contains the Universal Mobile Telecommunication System (UMTS) and Code Division Multiple Access (CDMA). 3G provide easy voice and data transmission to the end users. In order to provide these services 3G has improved the data transmission rate up to 144 Kbps in a high speed moving situation, 384 Kbps at a low speed moving situation and 2Mbps in a Immobile Situation. These 3G networks later developed into 3GPP, devotes the technologies recruitment of GSM and UMTS. The enhanced version of 3GPP is 3GPP2.

Introduction to IEEE 802.11 WLAN:IEEE 802.11无线局域网的介绍

WLAN referred as Wireless Local Area Network. The first WLAN created by IEEE in 1997. They called it as 802.11. The 802.11 protocol is used to connect wired and wireless network stations. It has two different types of protocol layers. They are PHY (Physical) layer and Media Access Control (MAC) Layer.

Media Access Control (MAC) Layer is a sub layer of Data link layer. It works as an interface between the physical layer and the logic link layer. It provides asynchronous data service and security service in 802.11.IEEE 802.11 has three various types of physical layers in this one is infrared and two RF transmission methods. The two RF transmission methods are direct sequence spread spectrum (DSSS) and frequency hoping spread spectrum (FHSS). The two RF transmission methods run with a rate of 2.4GHZ. DSSS uses two different shift keying techniques they are Different Bi and Quadrature Phase Shift Keying (DBPSK and DQPSK). The FHSS uses Gaussian frequency shift keying. Infrared layer is a multi directional layer served for the indoor purpose only operates on 4PPM (Pulse Position Modulation) and 16PPM. Another version of WLAN is 802.11b which is operates at same band 2.4GHz but uses another shift keying named Complementary Code Keying (CCK). IEEE 802.11a is an extension of 802.11 operates at 5MHz band. It utilizes OFDM (Orthogonal Frequency Division Multiplexing).

Integration of 802.11 WLAN and 3G:
It is challenging task to design a network architecture with capably integrates 802.11 and 3rd generation. The development of designing a network that permits users to switch between two different types of networks provides some advantages to both users and service providers by integrated 802.11/3G services. By combining of these networks they can attract more users and provide high speed with less data loss. There are several ways to interconnect these two wireless technologies namely

Tightly coupled integration
Loosely coupled integration
Peer integration
Mobile IP integration
Mobility gateway (MG) integration
The brief discription of these technologies are described below

Tightly coupled integration:
The major intend of the tightly coupled integration is to construct 802.11 network seems to 3G network as one more 3G network. Tightly coupled integration for WLAN/UMTS and WLAN/CDMA 2000 are explained below.

Interconnection between CDMA 2000 and WLAN:
In the Tightly coupled integration, a WLAN is treated as a 3G network by providing functions of 3G radio networks.

A CDMA2000 cellular network shown in Fig.2, several base stations (BSs) are associated with a RNC (radio network controller) via T1/T3 lines and the every RNC is connected to a PDSN (Packet Data Serving Node) through the PCF (packet control function). Purpose of the PCF is to manage the transmission of packets between base stations and the PDSN. Between a MS (mobile station) and the radio network controller (RNC), the Radio Link Protocol (RLP) distinct in the CDMA2000 standard is utilized to organize data transport between a MS and the RNC. On the other hand, the PPP (Point-to-Point Protocol) is engaged in between the PSDN and the MS. Multiple radio link protocol sessions between MS and the RNC are switched by the RNC to contribute the 144 Kbps carrier throughput in the 3G mobile networks. If a MS moves from one RNC to the other, the resultant radio link protocol session is detached and a innovative session requires to be established with the new RNC. The PDSN attach Internet. FA (Foreign Agent) function of mobile IP is executed in the Packet Data Serving Node for inter-PDSN mobility.

Interconnection between UMTS and WLAN UMTS和WLAN之间的互连

While integrating the UMTS cellular network and 802.11, Wireless LAN permits an mobile station to preserve connections to the Wireless LAN and UMTS concurrently: a packet data service during Wireless LAN and a circuit switched voice service through UMTS. UMTS provides services like PS (Packet-Switching), CS (Circuit-Switching) services and GPRS is integrated into UMTS for packet data service.

In UMTS, RNC and nodes B is include with RAN (radio access network) is called UMTS RNS. Each node B has a group of base stations. Several node B's attached to a RNC. The CN (Core Network) is consisting of serving GPRS support node (SGSN) and Gateway GPRS Support Node (GGSN). The RNC operates as a moderator for exchanging the RF (radio frames) to IP packets and vice versa via Serving GPRS Support Node. The IP packets are exhumed between Gateway GPRS Support Node and Serving GPRS Support Node and then between RNC and SGSNs. Some access points are associated to the IP routed network through Access Router (AR). When a mobile station moves across access points associated to the similar AR, intra-AR handoff takes place and is handled by the AR. During inter-AR handoff, the new Access Router executes the IP handover. Mobile IP switches any intra-domain mobility. The IP service layer is utilized to exchange the device detailed framework information with higher layers and also offers synchronization among the two device drivers. The IP layer protocols execute Resource Reservation Setup Protocol (RSVP) and Mobility Management Protocol (MMP) for Quality of Service signalling, reservation and mobility management in Wireless LAN network, correspondingly. The 802.11 device driver develops 802.11 MAC control functions and the UMTS device driver develops GPRS user and control plane protocols.

When an MS is influenced in UMTS, it obtains beacons from UMTS and thus make actives the UMTS interface, and if the mobile station is powered in 802.11, it can be attached to both 802.11 WLAN and UMTS. In this case, it accepts beacons from UMTS and 802.11. However, since UMTS supplies fundamental wireless service, it runs UMTS-GPRS power up method through UMTS interface disregarding the beacons from 802.11 interfaces. Behind UMTS power up procedure, the mobile station reacts to the 802.11 beacons by transmitting an association demand. After connected with the Access Point, UMTS-WLAN handover process handovers the PS connection to the WLAN network. In WLAN, the Mobile Station utilizes the similar IP address gained from Gateway GPRS Support Node in UMTS. The Mobile Station gets a temporary address which the packets are tunnelled using SGSN. In GPRS, the Packet Data Protocol (PDP) situation signalling is utilized to setting up a connection and reserves the possessions. The Radio Access Bearers (RAB) signalling is utilized to set up reserve radio resources and radio channels between RNC and SGSN. The Mobile Station corresponds with the SGSN for Packet Data Protocol perspective setup, which in turn organizes with the RAB and GGSN. In Wireless LAN, the RSVP is exercised for resource reservation. After the Mobile Station transmits a RSVP PATH message to Serving GPRS Support Node (SGSN), the SGSN consults the session setup with the Gateway GPRS Support Node (GGSN) using Packet Data Protocol context messages and reacts to the Mobile Station with RSVP RESV message. In Wireless LAN, the Mobile Station is connected to the General Packet Radio Service (GPRS) and preserves both UMTS and Wireless LAN mobility context. This structural design permits an MS to preserve a PS connection through Wireless LAN and CS connection via UMTS concurrently.

Loosely Coupled Integration:
In case of loose coupling integration, mobility management in the integrated WLAN/3G system is handled by use of MIP (Mobile IP protocols). The approach of loosely coupled integration is shown in Fig.2, in this Access Point (AP) connects a gateway, which connects the distributed system and next connects Internet. A Mobile Station is in touch with 3G by the use of Access Point (AP), gateway, distributed system and Internet. The gateway implements Mobile IP and AAA (authentication, authorization, and accounting) service to interwork through the 3G's home AAA servers. The authentication, authorization, and accounting (AAA) service allows exchanging billing information and accounting information in between the 3G network and a Wireless LAN.

The Packet Data Serving Node (PDSN) in CDMA2000 as shown in Figure 1 executes Mobile IP to maintain inter-PDSN handoff. The WLAN gateway in Fig.1 also wants to implement Mobile IP. The Mobile Station performs handoffs when its signal in one wireless network is weak or when it discovers a superior wireless signal in an additional wireless network.Benefits of the loosely-coupled integration consist of less complexity and low cost.

One disadvantage of the loosely-coupled integration is that it is very hard to provide Quality of Service assurance for time-responsive traffic because Internet Quality of Service (QoS) Itself is difficult to assurance.

Peer to Peer Integration:
In peer integration method the Mobile Internet Protocol (Mobile IP) is implemented, and users may utilize either the IEEE 802.11 Wireless LAN or UMTS. UMTS Core Network (UMTS CN) contains the Home Agent (HA) as well as functionality of authentication, authorization, and accounting (AAA) servers. In the 802.11 Wireless LAN (WLAN) and multiple ESSs (Extended Service Sets) are connected to AGW (Access Gateway). To support mobility to other peer networks the IEEE 802.11 WLAN contains Home Agent (HA) and as well as Home Location Register (HLR).

When the Mobile Station is subscribed to UMTS and when it visits an IEEE 802.11 WLAN network, the MS correlates with an Access Point (AP) first, after that executes AAA functions with a local AAA server. After successfully authentication the MS transmits a required Update to HA then the HA transmits required Acknowledgement to the Mobile Station. The Home Agent also handles the locations of the consumers by transmitting the location to the HSS (Home Subscriber Service), which terminates the connected SGCN and commences the new PDP. The packets pending to SGCN are routed to the MS and thus the following packets are also transmitting to the MS. The MS set up radio bearers for Universal Terrestrial Radio Access Network (UTRAN), when returning back to the UTRAN and executes UMTS connection followed by PDP activation. Thus it also achieves on the mobile Internet Protocol to inform the binding cache. When the MS is shifting the network that is the procedure of the hands-off, first transmits and connect agent of the UMTS and via the RAN (radio access network). The authentication, the billing mechanisms and mobility management have become reliable with the peer integration of the UMTS and WLAN. The main benefit of this integration is apart from the AAA servers everything is independent of each other.

When the Mobile Station is subscribed to an IEEE 802.11 network and when it visits an UMTS network, the Mobile Station set up UTRAN radio bearers and transmits an Attach message. The SGSN interrelates with the Home Location Register of IEEE 802.11 Wireless LAN to authenticate the Mobile Station, which after that carry out the PDP context commencement with the UMTS network. Thus Packets coming in IEEE 802.11 WLAN are routed to the GGSN and additionally routed to the Mobile Station. While it returning to the 802.11 WLAN, it associates with an Access Point and authentication, authorization, and accounting (AAA) functions are performed with the Home AAA server. The Mobile Station by exchanging required Update with the Home Agent (HA) and also transmits required Update to the preceding GGSN. The GGSN removes the PDP contexts and any packets to the MS are routed. Mobility Management methods construct the integration of 802.11 WLAN and UMTS more effectual.

Integration based on Mobile IP基于移动知识的集成

Mobile IP is employed when a mobile station roams from one network place to another. Outer surface of its home network, the MS is recognized by a COA (care of address). The MS registers its care of address with the Home Agent (HA). The HA exists in the home network of the MS and is responsible for interrupting datagram's addressed to the Mobile Stations home address. The datagram's to a MS are always routed through the Home Agent. Datagram's from the MS are transmitted along with best path by the Internet routing system and it employ reverse channelling through the HA. It is apparent that both networks are peer networks and the functionality of the Home Agent/Foreign Agent (HA/FA) exists at the IP layer.

The advantage of this integration is to makes the IP address mobile. The same IP address is utilized, which resolves the several address problems. The disadvantage of Mobile IPv4 is triangle routing and it might be defeat with the mobile IP with the use of optimized routing

Integration based on MG (Mobility Gateway):
The interconnection design is shown in Figure 4. An intermediate server (mobility gateway) is located in between the UMTS and IEEE 802.11WLAN sides and the MG (mobility gateway) will handle the mobility and routing issues.

When a mobile station (MS) is connected to an AP (access point), the communication path in between the CH (correspondent host) and MS on the Internet will be 1a to 3. The CH to MS communication path will be 4 to 2a. When the MS is on the UMTS network, this root will be 1b to 3, and the reverse root is then 4 to 2b. It must be observed that the part 3 and 4 in both roots do not modify regardless where the mobile station is positioned. Only the connections 1 and 2 will be frequently varying, depending on the movement of the MS. The communication between mobile station and the proxy server only is a subject to vary while preserving the proxy-CH connection unmovable supports mobility. The protocol design of the UMTS network is a adjustment of which the mobile gateway (MG) is located next to the GGSN part of the protocol stacks of the UMTS. On the MS, there will be several protocols assuming if the user wish for roaming between both networks when she or he is still in one of the network. So a dual-mode stack implementation function is required on the MS.

The main disadvantages of this architecture are it is not standardized therefore it needs proprietary protocols for roaming and the performance of a proxy is poor.

Vertical Handoff between UMTS and WLAN UMTS和WLAN之间的垂直切换

In vertical handoff technique the mobile stations use high-bandwidth Wireless LANs in hotspots and it changes to 3G mobile networks when the coverage of WLAN is not accessible or the network situation in WLAN is not enough. Virtual connectivity manager utilizes an end-to-end standard to sustain a connection without an extra network infrastructure support.

Horizontal handoff, described as a handoff between BSs (base stations) or between access points (APs), is very easy compared to vertical handoff, which has the following concerns when an mobile station travels from 3G to WLAN, the handoff can't be activated by the signal of the present system as in horizontal handoff and there is no similar signal strength accessible to assist the judgment as in horizontal handoff. Therefore, network situations such as obtainable bandwidth, delay and user predilections are utilized rather than the PHY layer limitations such as signal to interference ratio and received signal strength. Mobile internet protocol can be utilized for mobility management subsequent to a vertical handoff. The vertical and horizontal handoff techniques are shown below.

Conclusion 结论

As a conclusion, there was a more growth in the area of mobile communication system from the last few years. The imperfections that were there in 1st and 2nd generation mobile communication system have been defeated in the 3rd generation mobile communication system. The 3rd generation mobile communication system is a bit advanced when evaluated with the 1st and 2nd generation mobile communication system. In recent times there has been massive growth in the WLAN technology. To provide more benefits to the user and service providers, the service providers have to integrate both 3G and WLAN technologies. This concept examined and focused on the link layer and the network layer in order to reduce the effects on existing technologies and networks, particularly at the lower layers such as PHY and MAC. Based on the arguments offered for the specified interworking approaches, interconnection architecture based on mobile IP is selected as the most appropriate solution; because IP layer mobility management gives a capable way to interconnect varies packet oriented networks. Interworking can't be handled within a specific protocol of one network technology; it has to be handled on the existing layers above or a innovative layer has to be added exclusively for the reason of handling inter technology roaming.

Future directions 未来的方向

Present computer networks and telecommunications are on the limit of providing mobile multimedia connectivity, where mobile users would have access to remote information storages and computing services at everywhere. As an evolutionary movement towards the 4th generation (4G) mobile communications, mobility in varied IP networks with both UMTS and IEEE 802.11 WLAN systems is observe as one of the central concerns in making the 4G of telecommunication systems and networks.

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