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Summary HSDPA, WiMAX and LTE are present technological focuses, this text analyzes and compares the three from several respects such as modulating, retransmission, network connection way and technological maturing status, and provide the corresponding conclusion.

With the fast development of mobile communication and Internet, the market of communication is demonstrating the speech business to move and melt, development trend with broad band data traffic. By the end of 2007, the number of users of China Mobile has already been close to 500 million, the number of users of Internet's Broadband has already exceeded 100 million. In the newly-increased Internet user, 63% are Broadband users. Meanwhile, technical development such as WiFi, GPRS, EDGE, cdma1x make the wireless data traffic employ extensively day by day.

HSDPA and WiMAX, as offering two kinds of technology of moving data traffic at a high speed, is causing the increasingly much attention. And LTE has caused everybody's extensive concern as 3G long-term gradual progress scheme. Though LTE is 3G next gradual progress direction, it has adopted many kinds of new technologies, especially there are revolutionary changes on the physical layer, changes on the network architecture greatly, it has very great development in direction of doing away with a hierarchical system.

From market orientation, WiMAX and HSDPA offer the high-speed data traffic, it is excursive to all support at the same time, so both there is certain competitive relation. But both there are its own technological characteristics, so can complement one another to a certain extent still. Though LTE is still at the standard to study stage at present, as the developing direction of future 3G, need the operator to pay the sufficient attention. This text is from modulating, retransmission, network connection way and technological maturing status,etc., several respects, analyze and relatively offer reference for the fact that the next step is chosen in gradual progress of the network and technological scheme to the three.

1,Modulation technique

In order to meet the constantly changeable radio path, HSDPA, WiMAX and LTE have all adopted many kinds of modulation modes, can change the modulation mode dynamically according to the change of the quality of radio path at the same time, so that the transmissive characteristic is optimum. WiMAX has adopted BPSK, QPSK, 16QAM and four kinds of adjustment ways of 64QAM, and HSDPA has adopted QPSK and two kinds of modulation modes of 16QAM. 802.16 serial standards have stipulated under different channel bandwidth, in the system in order to meet requirements for bit error rate of 10-6, various modulation and encoder mode required lowest signal intensity. As to HSDPA system, 3GPP norm defined different terminal stations of 12 kinds of ability. Have stipulated 30 kinds of CQI classifications in unison to each kind of terminal station. And this different CQI ranks reflect different signal channel quality conditions, corresponds to a kind of transmission format at the same time, and stipulated separately the block size of transmission, code rate, modulation mode, code channel used are counted etc.. LTE supports to be up to the modulation mode of 64QAM, adopts CQI way at the same time, utilizes terminally to report wireless network quality, the network reports to value for decision and adopts the corresponding network parameter according to it, and then determine the final message transmission rate.

In the technology of physical layer, HSDPA adopts the single carrier CDMA way to insert. And WiMAX adopts the way of the multi-carrier, the data are modulated to and assigned on the machine format subcarrier according to increasing progressively the order according to the code number of frequency swing after interweaving and constellation mapping. Should be modulated from the first symbol that is sent in the constellation mapping device of the data to have on the subcarrier that low frequency leans towards the code most number. WiMAX still allowed to use OFDMA to insert at the same time, all these improved the utilization factor of frequency of WiMAX system to a certain extent. The scheme of descenting of LTE standard includes OFDMA and MC-WCDMA. OFDMA is the physical layer technology that is most likely adopted at present. And the up run includes SC-FDMA and two kinds of access ways of OFDMA. LTE confirm, adopt many the intersection of aerial and technology already, the intersection of MIMO and aerial basic disposition of number to descent 2& times among them; 2,Upstream 1& times; 2,But is considering 4& times; 4 high-order aerials are disposed.

2,ARQ mechanism

Because the wireless moves the signal channel and has time varying and multipath decline characteristic that causes, often have higher bit error rate. So in order to reduce the retransmission on the senior level, improve the probability received correctly and reduce time delay, WiMAX, HSDPA and LTE all adopt forward error correction (FEC) And automatic retransmission is asked (ARQ) Two kinds of mistake control methods, in order to guarantee the service quality (QoS) ,HSDPA and LTE go still one step further to adopt HARQ mechanism.

In ARQ mechanism, are having 4 kinds of states to send a ARQ piece of side: Have not sent, been immature, waited for retransmission and abandoned. The conversion between these 4 kinds of states is shown as in Fig. 1.

3 standard ARQ the intersection of SAW and the intersection of person who park and agreement in agreement, GBN go back the intersection of go-back-N and agreement and SR selective retransmission agreement, in 3 kinds of ARQ basic mechanisms, the agreement is simplest that SAW stops,etc., require the minimum agreement to the letterhead too. Make a start and deal with present packet until it has been succeeded in receiving all the time in its characteristic. Agreement exactness by bit ( Used for showing at present and next packet) Information can be stated. So, its control head is very small, it is very small to confirm the head. And because can only convey a packet once, the requirements for the user memory capacity are very small. Making a start and can be sending a plurality of packet continuously by GBN way. Needn't wait for the acknowledgement of receipt after making a start and sending dividing into groups first, through after a round delay, this acknowledgement of receipt that divides into groups just arrives and makes a start. The round delay is defined one as sending dividing into groups to and receiving the time interval during its acknowledgement of receipt. In time interval this, N-1 piece divide into groups, convey in addition. When what the receiving end is feedbacked back is NAK, make a start and retreat correspondent grouping of this NAK, send again one of this dividing into groups and subsequent N-1 and divide into groups. Because GBN way adopts serial sending and retransmission, has raised the efficiency of stopping equality, and the receiving end only needs to store and divide into groups at present. But as the round delay is larger, at the time of the great of message transmission rate, because of wanting retransmission not to divide into groups by mistake, GBN way is not very effective. SR agreement is the most effective by contrast, but it is complicated to require memory capacity to be very great and realize. Its characteristic only conveys wrong packet, requires that discerns packet with the sequence number. Moreover, when waiting to respond to, in order to fully utilize channel capacity to make a start and send a large amount of packet. In addition, the receive side must know the sequence number before making those information of separating retransmission up, so sequence number want the intersection of data and code of parting, and sequence number need reliable code in order to overcome, appear mistake into data any time, increase the bandwidth required to the signalling in this way.

The advantages of HARQ technology comprehensive FEC and ARQ two kinds of mistake control modes have overcome their own shortcomings, carry on the appropriate association of the two, enable SW-ARQ, GBN-ARQ or SR-ARQ system imbeds a FEC subsystem, form HARQ system. HARQ technology is divided into type-I and type-II at present. And HSDPA system mainly adopts Chase based on RCPT yard to amalgamate the method and increases progressively the redundant method and realizes type-II HARQ technology.

3,Mechanism of scheduling of resource

For can efficient the intersection of use and Radio Resource RR, HSDPA, WiMAX, LTE adopt effective the intersection of scheduling of resource and mechanism.

The MAC layer of WiMAX supports the multi-point Broadband wireless access application of dot pair, mainly carries on high-speed transmission on up run and downlink. In order to let a plurality of users share a physical signal channel, the MAC layer must have valid access and bandwidth assignment algorithm in order to support QoS of different business to guarantee. Each connection is associated with single data traffic, each data traffic is associated with a series of QoS parameter, these QoS parameters have quantized the behavior of the data traffic. These parameters are managed through DSA and DCS news dialogue. The standard supports 4 kinds of different types of traffic, they serve for authorizing voluntarily (UGS) respectively , real-time roll polling business (rtPS) , non- real-time roll polling business (nrlPS) , the transmission service of doing the best (BE) . WiMAX can have greater flexibility according to different bandwidth of QoS dynamic assignment. The MAC layer of WiMAX is based on connecting, in order to shine upon each subscriber station (SS) Service,it is to offer different stage QoS,the all one data communication is based on the fact that connected. So, the traffic flow is offered the mechanism of ascending-descending QoS management in fact, and and the assigned process of bandwidth is contacted closely. One SS asks the upstream bandwidth in such a manner that on the basis of each connection. BS in the dispatcher interval of a certain time, or ask to always award a bandwidth all of one SS, or award the bandwidth according to each connection. So can be found out from the above-mentioned analysis, WiMAX can offer the service of different quality for different business in the radio network part.

HSDPA can adopt many kinds of resource dispatch algorithms, there are different characteristics on efficiency and service fairness In Service in each kind of algorithm. These algorithms include the roll polling type dispatch algorithm, fair throughput dispatch algorithm, C/I dispatch algorithm, maximum C/I dispatch algorithm, some fairness dispatch algorithms and fast fair throughput dispatch algorithms on average, among them not consider the change of the quality of signal channel in the first 3 kinds of algorithms, and then 3 kinds of changes consider the change of the signal channel environment, adjust and distribute the tactics according to these changes at the same time.

The roll polling type dispatch algorithms, to user's fair service of all activation, the users in different positions of Residential Area will all wait for probabilistic acquisition Radio Resource RRs. The lowest users of throughput at present of prior choice of dispatch algorithm of fair throughput. The average C/I dispatch algorithm chooses the users of average C/I value maximum to serve within one dispatching cycle. The C/I type dispatch algorithm of maximum chooses the preferably user of the wireless environment in one TTI is separated by how to serve, this kind of method changes to the radio path correspondingly fast, can obtain the throughput characteristic of Residential Area of maximum, but the fairness is discrepancy. Some fairness dispatch algorithms trade off, consider synthetically users live in wireless environmental quality and historical throughput situation at present, choose the user with better mass rotio how to serve. Fast fair the intersection of throughput and dispatch algorithm take to change characteristic to try hard, offer fair throughput to inner all users in the Residential Area, distribute while fast signal channel into consideration.

LTE ensures the high-efficient operation of the network by many kinds of scheduling of resource way, mainly includes the following respects.

( 1) Wireless to bear the weight of and control (RBC) ;

( 2) Wireless to admit and control, (RAC) ;

( 3) Connect excursively and control (CMC) ;

( 4) Divide into groups and manage (PSC) ;

( 5) The interference of the minizone is coordinated(ICIC) ;

( 6) Load is balanced (LB) .

4,Network architecture

The network architecture of WiMAX is shown as in Fig. 2, including the access network (ASN) And connection service network (CSN) . The function of ASN is to manage the air interface. The main function is including finding the network and choosing appropriate CSN; And move the subscriber switchboard (MSS) in the base station During setting-up layer 2 connect; Assist to finish authenticating, business to authorize and charge; Assist high level and MSS to set up the connection of layer 3, distributes the IP address; Wireless resource management; Carry on the Mobility Management in ASN according to hierarchy; Paging and position are managed in ASN; The tunnel is set up and managed between ASN and CSN; Store temporary FYI. One ASN is by the base station (BS) And insert the gateway (ASN GW) The group, can be connected to a plurality of CSN, provide service for CSN of different NSP.

CSN offer IP to WiMAX user connect, as one association of network function, including Internet inserts mainly; Offer conversation to user to connect; QoS and permission based on user's parameter control; Setting-up and management of the tunnel between ASN and CSN; Users charge and settle; Mobility Management between ASN; WiMAX service,etc.. CSN can be acted for by router, AAA or server, user's database, Internet gateway device,etc. make up. CSN can also utilize the existing network equipment to realize CSN function partly as a newly-built Network Entity NE of the brand-new WiMAX system.

UMTS basically forms and is shown as in Fig. 3, the core network divides for the circuit land (CS) And the packet field (PS) . The internetworking unit includes the switching center of mobile service (MSC) , visit location register (VLR) , Gateway Mobile Switching Center (GMSC) ,The internetworking unit of packet field that HSDPA uses includes the business GPRS supporting node (SGSN) , Gateway GPRS Support Node (GGSN) ,Attaching position register (HLR) , authentication center (AuC) And equipment identification register (EIR) Share the network element for circuit land and packet field. The internetworking unit of the wireless access network includes the wireless network control center (RNC) And the message transmitting/receiving base station (Node B) of WCDMA Two parts. In addition the core network PS land inserts other PLMN networks or PDN networks through Gi, Gp interface, insert fixed network or other PLMN through PSTN in CS land. RNS (wireless network subsystem) Pass the air interface (Uu) Connected to mobile station directly, is responsible for sending receiving and wireless resource management of the wireless signal. On the other hand, RNS links with MSC, SGSN, realizes the mobile subscriber or mobile subscribers connects with communication between rigid network users, signal and FYI of the conveyor belt,etc.. RNS subsystem includes two parts of RNC and Node B.

LTE compares WCDMA (HSDPA) The network has adopted the network framework of doing away with a hierarchical system, this respect has reduced the quantity of the apparatus, reduced the time delay of the business greatly at the same time. LTE network framework shown as in Fig. 4.

Among them: ENode B main function include wireless resource management, wireless to bear the weight of, control, not wireless to accept, control, connect excursive control and dynamic resource allocation ' Deployment) .

And aGW in fact includes some functions in all functions in GGSN and SGSN and RNC in 3G network. Among them increased newly MME function is used mainly in the distribution to the paging news of eNode B, and UPE function is used in IP header compression and user's data encrypting, the end of the data packet of the User plane and support UE excursive machine format exchange of User plane. About division of the function in aGW and eNode B of RNC function, very great dispute has existed all the time, by 2007, the latest LTE standard develops and adopts two Layer network frameworks for the future 3GPP system, header compression and cryptographic function up-shift that lay in RNC originally got to insert the gateway, Outer ARQ and RRC function downward shift was to eNodeB, shown as in Fig. 5 specifically.

5,Conclusion

This text, from many kinds of critical technology to HSDPA, WiMAX and LTE have been compared with and analyzed. In order to offer the high-speed data traffic under the moving environment, the three have all adopted some critical technology, use many kinds of modulation modes, can adjust the modulation mode according to change of the quality of radio path at the same time. 160AM to compare HSDPA, WiMAX and LTE can support 64QAM while being highest, support OFDM. On network architecture, the intersection of network connection and way of WiMAX seem flexible, each ASN can at the same time for belong to different CSN of NSP, serve. And HSDPA concrete defining technically is more careful, for example raise transmissive efficiency on the reselection mechanism with HARQ, what Mobility Management is done is better at the same time. LTE has adopted the network framework of doing away with a hierarchical system, is reducing the system equipment to reduce the time delay of the business to improve a lot. On system performance, in case of bandwidth of 5Mbit/s, HSDPA highest achievable about 15Mbit/s of speed, and WiMAX and LTE allow to use larger bandwidth, because of adopting OFDM technology at the same time, the spectral utilization factor of the two is higher.

In maturing status of products, HSDPA technological maturing status is the highest, had over 100 business networks already. The apparatus of 802.16D can already be realized commercially in WiMAX, 802.16E apparatus can basically be realized commercially in 08, by June of 2006, carry on WiMAX test and offer the commercial the whole world of operator to already exceed 150, it exceeds 20 to enter the commercial network. And LTE distance is commercial also takes some time. WiMAX has already been included in 3G standard at present, there are certain advantages in the high-speed tetherless access respect at the same time, but HSDPA is based on the Off-The-Shelf 3G network framework, considers in excursive, user's management and network management,etc. more overallly. In sum, HSDPA and WiMAX have adopted many kinds of advanced technique, the access speed of the mobile communication data traffic of great amplitude enhancement, and LTE has drawn the technological advantages of HSDPA and WiMAX, accords with 3GPP standard at the same time, it is the direction of mobile communication network development in future, so should positive canonial development, LTE of tracing, development of the network lay the good foundation for future.