Differences between WCDMA and LTE

CDMA2000、WCDMA and TD-SCDMA All are 3G Air interface standard , The access standards are different .
H/V&jTy among WCDMA It's using FDD, Unwanted GPS Support for ; TD-SCDMA It's using TDD, need GPS Support for , Such as smart antenna 、 many User detection 、 Relay switching and other new technologies . be relative to WCDMA Come on ,TD It does not support normal services for users in high-speed motion . But because of the smart antenna , It can reduce the system overhead and expand the coverage ; use TDD Operation mode , Improved frequency utilization of resources . wait .

WCDMA and LTE The main difference between the air interface and the physical layer , The difference of the physical layer affects the upper layer MAC,RLC The difference in waiting .

In general structure ,WCDMA and LTE The air interfaces of are all called UU mouth , But the biggest difference in the protocol stack is that LTE Of UU There is no in the port protocol stack BMC This entity . because LTE Adopt all IP Architecture , Cancel CS Domain , The voice telephone is carried in PS On domain , That is to say VOIP. and BMC The main functions of the MBMS Realization .

I only study FDD,TDD Don't know much about it ,
The physical layer is the biggest difference ：
W It adopts code division multiple access technology ,5MHz One band . In the downward direction , Different channels use different spreading codes , Different cells use different scrambling codes distinguish ; In the upward direction , Different services of the same user are distinguished by spreading codes , Different users are distinguished by scrambling code . For all users , What we can use is the resources in the frequency domain . Physical channel adopts 10ms Wireless frame format , Each wireless frame has 15 A time slot .

L It's using OFDMA, That is, orthogonal frequency division multiplexing , Divide the available bandwidth into several 15K The subcarriers of . arbitrarily 2 The subcarriers are orthogonal . Also used 10ms Frame of , Divide into 10 Subframe , Each subframe 2 A time slot . Upload each time slot 6 Or 7 Symbols . Whether up or down ,UE The resources that can be scheduled and used by the BTS are RB.RB It is a concept in time and frequency domain , One in the frequency domain RB The bandwidth of is 12 Frequency band width of subcarriers , That is to say 180KHz; In time domain , Is the time interval of a time slot , That is to say 7 Symbols . From this division , You can work it out by yourself LTE Approximate peak rate of . The system can schedule one or more per user RB, The more you schedule , The higher the data transmission rate .

Because of the adoption of OFDMA technology , Therefore, the change of frequency has a great impact on the whole system , So we used CP To reduce the inter carrier interference .

about WCDMA and LTE Interference suppression of the system , Personal opinions are as follows ：-WCDMA Uplink data transmission R99 still HSPA The air interface , Are based on dedicated channels . therefore Multiple access interference exists among uplink multiple users . And because WCDMA The characteristics of single frequency distribution network , bring UE Uplink data transmission is generated intra-cell interference There may also be inter-cell interference. Solutions to uplink multi-user interference , To counteract with interference （SIC and PIC） As a representative .
-LTE The uplink of is designed as shared, orthogonal uplink. in other words , Uplink of the same cell active users Each takes up a different time alignment sub-band. So the upward intra-cell interference Not the main problem . but inter-cell interference It is still possible . This interference can be mitigated in many ways , If... Is adopted in the uplink hopping.inter-cell interference It may also exist in the downward direction （ Single frequency network ）, Even though eNodeB A flexible radio resource management method can be used to inform the subcarrier information sent to the cell edge users neighbour cell(eNodeB) To mitigate possible interference conflicts , But because LTE It is generally considered to be conducive to providing high-speed data transmission ( Which means more power ）, Therefore, the influence of interference cannot be ignored . stay LTE in , The problem of CO frequency interference is worth studying .

From the physical layer ,PCI（physical-layer Cell identity） By the main synchronization signal （PSS） Synchronizing with the secondary signal （SSS） form , Can be obtained by simple operation . The formula is as follows ：PCI=PSS+3*SSS, among PSS The value is 0...2（ It is 3 Species difference PSS Sequence ）,SSS The value is 0...167（ It is 168 Species difference SSS Sequence ), Using the above formula, we can get PCI The scope of is from 0...503, So there is... In the physical layer 504 individual PCI.
Actually , You can put PCI Understood as scrambling code , As in the WCDMA The downlink scrambling code in the system is used to distinguish sectors , Scramble the data to be sent , So that the terminal can distinguish different sectors .
    From the perspective of network operation and maintenance level ,CI（Cell Identity） Uniquely identifies a cell , Cannot repeat in the network . but PCI But it can be repeated , because PSS+SSS have only 504 Combinations of . Such as , When there is 1000 When you are in a community ,PCI have only 504 individual , At this point we need to be right PCI Reuse , Usually ,PCI The planning principle is that each sector is assigned a specific PSS Sequence (0...2) value , Each base station is assigned a specific SSS Sequence （0...167) value , In order to avoid the same between adjacent base stations PCI The problem occurred .