CDMA vs LTE system architecture

Comparison of CDMA and LTE architectures

CDMA (IS-95/CDMA2000) is a 2G/3G hierarchical, circuit-switched architecture; LTE (4G) is a flat, all-IP, packet-switched architecture.

 CDMA (CDMA2000 1x)
 [MS]~~[BTS]--[BSC/PCF]--[MSC]--PSTN
                  |        |-[HLR/AuC] [VLR]
                  +--[PDSN]--IP net (AAA, HA)

 LTE (EPS)
 [UE]~~[eNodeB]==X2==[eNodeB]
          |S1-MME   |S1-U
        [MME]----[S-GW]--S5--[P-GW]--Internet
          |                    |
        [HSS]               [PCRF]

Functions of CDMA entities

• MS: user terminal; does spreading, RAKE reception and power control.
• BTS: radio transceivers, spreading/despreading, pilot transmission.
• BSC: radio resource management, soft handoff (frame selection/distribution), vocoding, power control.
• MSC: call switching, mobility, link to PSTN; HLR/VLR/AuC store subscriber data, location and keys.
• PCF/PDSN (CDMA2000): packet control and gateway to IP networks; AAA for authentication/billing and HA for Mobile IP.

Functions of LTE entities

• UE: user equipment with USIM.
• eNodeB: the only radio node; radio resource control, scheduling, header compression, ciphering, handoff decisions; eNodeBs linked by X2.
• MME (Mobility Management Entity): control plane – attach, authentication with HSS, tracking area updates, paging, bearer setup, S-GW selection.
• S-GW (Serving Gateway): routes user packets; mobility anchor during handoff between eNodeBs.
• P-GW (PDN Gateway): connects to external IP networks; IP address allocation, policy enforcement, charging.
• HSS (Home Subscriber Server): subscriber database (like HLR + AuC).
• PCRF: policy and charging rules (QoS).