3g

3G:

3G

3G:

3G wideband CDMA CDMA2000 the Universal Wireless Communication (UWC-136) interfaces

Major Air Interfaces Evolution:

Major Air Interfaces Evolution 2G Technology 3G Technology IS-95 CDMA GSM IS-136 TDMA cdma2000 W-CDMA UWC-136

Evolution towards 3G:

Evolution towards 3G

Cell Stucture:

Cell Stucture The 3G network might be divided up in hierarchical fashion: Macro cell - the area of largest coverage, e.g., an entire city. Micro cell - the area of intermediate coverage, e.g., a city centre. Pico cell - the area of smallest coverage, e.g., a "hot spot" in a hotel or airport

ARCHITECTURE:

ARCHITECTURE 3G wireless networks consist of Radio Access Network (RAN) A core network Intelligent Network

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3g architecture

RAN:

RAN RAN functionality is independent from the core network functionality The Radio Access Network consists of new network elements, known as Node B and Radio Network Controllers (RNCs) Node B - Base Transceiver Station RNC replaces the Base Station Controller

CN – Core Network:

CN – Core Network The CN is a network located between RAN and another network[e.g. PSTN] Composed of – Circuit Switches (MSC / GMSCs) Packet Switches (SGSN / GGSN) Subsriber database (HLR / VLR) Address Resolution servers for packet processing (DNS) Authentication and Security Centres ( AuC / EIR)

IN – Intelligent Network:

IN – Intelligent Network The Intelligent Network is a node group for achieving enhanced services (number portability, freephone, credit cardcalls etc) It is composed of various Service Control Points(SCPs)

TDD vs FDD:

TDD vs FDD Wireless duplexing has been traditionally implemented by dedicating two separate frequency bands: one band for the uplink and one band for the downlink (this arrangement of frequency bands is called paired spectrum ). This technique is called Frequency Division Duplex, or FDD. The two bands are separated by a "guard band" which provides isolation of the two signals:

FDD:

FDD

TDD:

TDD the uplink and the downlink operate on the same frequency, but they are switched very rapidly: one moment the channel is sending the uplink signal, the next moment the channel is sending the downlink signal. The switching is performed very rapidly, thus, it appears that one channel is acting as both an uplink and a downlink at the same time.

Need for TDD:

Need for TDD FDD transmission is not so well suited for asymmetric applications as it uses equal frequency bands for the uplink and the downlink (a waste of valuable spectrum). On the other hand, TDD does not have this fixed structure, and its flexible bandwidth allocation is well-suited to asymmetric applications, e.g., the internet

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TDD mode does not allow long range transmission (the delays incurred would cause interference between the uplink and the downlink). For this reason, TDD mode can only be used in environments where the propagation delay is small (pico cells).

3G Spectrum:

3G Spectrum UMTS FDD is designed to operate in paired frequency bands, with uplink in the 1920-1980 MHz band, and downlink in the 2110-2170 MHz band. UMTS TDD is left with the unpaired frequency bands 1900-1920 MHz, and 2010-2025 MHz.

Packet Processing in IMT -2000:

Packet Processing in IMT -2000 WCDMA : Same as that for GSM. Mobility management is done using HLR and VLR.

Packet Processing in IMT -2000:

Packet Processing in IMT -2000 CDMA2000: Uses the MobileIP system When a user moves to a foreign network a care of address is sent from the Foreign Agent (FA) in the Foreign Network to The Home agent (HA) in the User’s home network. The Packets for a moving user are re-forwarded to the FA by the HA according to the care-of address.

Adaptive Modulation and Coding:

Adaptive Modulation and Coding AM & C is a technique for adapting the modulation and coding based on the received signal quality and channel conditions. Users close to the Base station are typically assigned a higher order modulation with higher code rates. Modulation order and code rates decrease as the distance from the BS increases. This requires feedback from the receiver about Signal Quality.

Hybrid ARQ:

Hybrid ARQ ARQ is an indispensable function for error free data transmission and is usually handled in the TCP layer to establish reliable end-to-end link communication. When a wireless link is used in aprt of the connection frequent retransmissions between hosts due to transmission errors reduces the throughput and delay performance

Hybrid ARQ:

Hybrid ARQ HARQ is a technique which combines ARQ with forward error correction (FEC) functionality. FEC decoding using soft combination of retransmitted data with the data transmitted first can improve the error correction performance and reduce the no. of retransmission attempts. Additionally Local ARQ in the wireless link may also be used.

Fast Cell Site Selection:

Fast Cell Site Selection To receive a frame, a mobile station selects the cell site that is best able to transmit the required data and then requests the selected cell site to transmit it. The other cells which are not selected by the mobile stations switch off their transmitters. This process is repeated every frame.

Transmission Power Control:

Transmission Power Control The transmit power required is estimated using path loss derived from RSSI at the receiver. For dedicated Lines a target BER is set and using this BER the transmission power is calculated. These Power schemes reduce average amount of unnecessary power wasted in transmission. Moreover, the Interference is reduced.

Antenna Diversity Schemes:

Antenna Diversity Schemes A space diversity antenna with large inter-element spacing in antenna arrays. Small interelement spacing in array elements. The spatial coherence is very high and the configuration results in beamforming. Space diversity array in which each diversity branch consists of a sub-array, thus combining space diversity and beamforming.

Seamless roaming – using MobileIP:

Seamless roaming – using MobileIP

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Env 1: User connects to an application server in the Office using a portable device and is assigned a private IP. Env 2: User moves out of the office for a meeting. Thus, the user is mobile on a road with no coverage from the office network and is handed over to an IMT 2000 3G network. Env 3: User reaches the meeting spot i.e. a WLAN hotspot. The User is automatically switched to the WLAN network offering a stronger signal than the 3G network. MobileIP integrates all the bearer services to provide seamlesss mobility.

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Thank you!