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Showing posts with label LTE. Show all posts
Showing posts with label LTE. Show all posts

Thursday, September 6, 2012

3G LTE Requirements, Network and Protocol Architecture, Channel Mapping and UE Categories, TCP Throughput vs Round Trip Time (RTT) , Why 3G LTE

3G LTE Requirements
 
Spectrum efficiency

DL : 3-4 times

UL : 2-3 times

Frequency Spectrum

Scalable bandwidth : 1.4, 3, 5, 10, 15, 20MHz

To cover all frequencies of IMT-2000: 450 MHz to 2.6 GHz

Peak data rate

DL : > 100Mb/s for 20MHz spectrum allocation

UL : > 50Mb/s for 20MHz spectrum allocation

Latency

C-plane : < 100ms to establish U-plane

U-plane : < 10ms from UE to server

Coverage

Performance targets up to 5km, slight degradation up to 30km

Mobility

LTE is optimized for low speeds 0-15km/h but

connection maintained for speeds up to 350 or 500km/h

Handover between 3G & 3G LTE

Real-time < 300ms

Non-real-time < 500ms

LTE is aimed at minimizing cost and power consumption while ensuring backward-compatibility and a cost effective migration from UMTS systems. Enhanced multicast services, enhanced support for end-to-end Quality of Service (QoS) and minimization of the number of options and redundant features in the architecture are also being targeted.
The spectral efficiency in the LTE DownLink (DL) will be 3 to 4 times of that of Release 6 HSDPA while in the UpLink (UL), it will be 2 to 3 times that of Release 6 HSUPA. The handover procedure within LTE is intended to minimize interruption time to less than that of circuit-switched handovers in 2G networks. Moreover the handovers to 2G/3G systems from LTE are designed to be seamless.

 
Why 3G LTE?


 Market Trends

    The trend of the market is an increase and an acceleration of the data
    mobile traffic in the next years.
    This has been possible thanks to the introduction of:
    ->EV-DO with CDMA2000
    ->HSDPA and HSUPA with WCDMA 

     Mobile phone user population is estimated to increase to 4 billion by 2011.
    Fixed Broadband application, massively adopted, can be exported to the mobile environment.
    The millennial generation will spread in the next years their “early adopters” way of life.
    The richer ecosystem of devices allows one to be connected all the time: PDA, laptop, mobile phone, USB device

With the recent introduction of HSDPA and EV-DO Rev A, there has been a significant increase in mobile data
traffic, with some operators quadrupling their Packet Switched traffic in one year. At this growth rate, and
with the proliferation of new applications on the network, cells in hot pots will be quickly saturated and the
network will require densification in these overloaded areas. This can be delivered by using a higher capacity
solution such as LTE. Mobile traffic growth is illustrated on this slide: mobile data traffic (in Gigabits per
year), with a typical operator in a western country with a 60 million population.

LTE TCP Throughput vs Round Trip Time (RTT)

The Transmission Control Protocol (TCP) is designed to provide reliable transport for packet data.

Today TCP is used for 80-90% of all packet traffic in the internet.

TCP is typically used in applications where reliability is important and some delay can be tolerated (web browsing, Email, FTP).



                                X2 Latency Aspects

U-plane

–X2 latency should be less or equal than radio link interruption time during HO (30…50ms) for optimum performance

–X2 latency significantly less than radio link interruption time would have no benefit

C-plane

–3GPP 36.423 defines X2 C-planes timers, giving implicitly an upper bound for the X2 transport RTT (50ms default, configurable 10…2000ms)

 LTE Possible Dimensioning Concepts

All-Average

–The backhaul connection shall support the aggregated average capacity of all cells. The average capacity is determined under realistic air interface conditions and multiple users per cell.
 

All-Average/Single-Peak

–The backhaul connection shall support the aggregated average capacity of all cells, while at least supporting the peak capacity of one cell.
 

All-Peak

–The backhaul connection shall support the aggregated peak capacity of all cells (“non-blocking”). The peak capacity is determined under ideal air interface conditions and with a single user per cell. This approach will lead to over-dimensioning, thus usually extra costs.


LTE Channel Mapping and UE Categories

  1.     Logical and transport channel mapping in downlink and uplink
  2.     LTE UE Categories


   
LTE Network and Protocol Architecture

  1.     LTE/SAE network architecture
  2.     EPC -Evolved Packet Core
  3.     Base Station control plane and user plane protocol stacks
  4.     EPC protocol stacks




Question and answer
  • How to do project based on cross layering of Physical and Mac layer to determine QoS in terms
    throughput,delay packet loss ,packet error rate.

    what concept and formulas are required to implement the proportional fair, channel aware scheduling algorithm in LTE.

    Answer
  • In the IEEE papers they have implement algorithm and with mathematical formulas or model for each with scheduling concept. In this paper they have implement scheduling in 4g "Simulating LTE Cellular Systems: an Open Source Framework" Giuseppe Piro, Student Member, IEEE, Luigi Alfredo Grieco, Member,
    IEEE, Gennaro Boggia, Senior Member, IEEE, Francesco Capozzi, Student Member, IEEE, and Pietro Camarda

Saturday, September 1, 2012

simulation suite including link-level (LTE PHY Lab) and system-level (LTE MAC Lab) LTE simulators running under MATLAB environmen

LTE LAB™



banner
LTE LAB™ is a complete simulation suite including link-level (LTE PHY Lab) and system-level (LTE MAC Lab) LTE simulators running under MATLAB environment. LTE PHY Lab is a comprehensive implementation of the 3GPP Release 8, 9 and 10 E-UTRA physical layer. LTE MAC Lab truly reflects the dynamic behavior of a modeled radio access network focusing on Radio Resource Management features such as scheduling and link adaptation and including implementation of propagation and mobility models.

Downlink E-UTRA processing chain

Downlink channels and signals

Transport channels
and control information
Physical channels and signals
Rel. 8, 9
and 10
DL-SCH, BCH, CFI, HI, DCI PDSCH, PBCH, PDCCH, PCFICH,
RS, P-SS, S-SS
Rel. 9 and 10 CRS, PRS, CSI-RS, UE RS

Uplink E-UTRA processing chain

http://is-wireless.com/images/images/LTE_MAC.png

Uplink channels and signals

Transport channels
and control information
Physical channels and signals
Rel. 8, 9 and 10 DL-SCH, BCH, CFI, HI, DCI PRACH, PUSCH, PUCCH, DRS for PUSCH,
DRS for PUCCH, SRS
Rel. 9 and 10 PUCCH format 3

3GPP Rel. 8 Features (LTE PHY Lab)

  • 3GPP Release 8 E-UTRA physical layer implementation according to TS 36.211-870, TS 36.212-870, and TS 36.213-870
  • Downlink and uplink (including RACH) support available from day one
  • FDD duplexing, TDD – available on request
  • Support for MIMO (2 and 4 antennas SM (SU-MIMO), TX diversity), OFDMA and SC-FDMA
  • Support for all the LTE bandwidths: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, 20MHz
  • Flexible control of all the necessary parameters
  • Channel models included (AWGN, SUI, E-UTRA 3GPP TS 36.101)
  • Test files included

3GPP Rel. 9 and 10 Features (LTE PHY Lab)

  • Support for Carrier Aggregation for up to 5 Carrier in Downlink and 5 Carriers in Uplink
  • Extended Downlink SU-MIMO (with up to 8 antennas)
  • Uplink SU-MIMO (with up to 4 antennas)
  • Uplink Spatial Diversity for PUCCH
  • New PUCCH format 3 for Carrier Aggregation
  • Support for Normal and Extended Cyclic Prefix
  • Release 9 positioning reference signals
  • Release 10 extended UE specific reference signals
  • CSI Reference signals
  • Clustered SC-FDMA
  • Possibility for simultaneous transmission of PUCCH and PUSCH in the same component carrier
  • Flexible control of all the necessary parameters, including: number of Component Carriers, MIMO configuration for Downlink and Uplink, RS configuration, PUCCH format selection

System-level Simulator Features (LTE MAC Lab)

  • Environments: Rural, Urban, Suburban;
  • Pathloss models : Modified Okumura – Hata model, 3GPP TS 36.942 Model, Winner Model, COST 231 Model;
  • Multipath models: 3GPP TS 36.942 Model, Winner Model, Random Distribution Model;
  • Users Mobility Models: Random Direction Model, Random Way Point Model;
  • Antenas Characteristic Model; Omnidirectional Characteristic, 1 or 3 Sectors Characteristic
  • RRM Functionalities: scheduling (PF, RR, max CQI), link adaptation
  • LTE channel bands: 900MHz, 1800MHz, 2100MHz, 2500MHz
  • All LTE bandwidths: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, 20MHz
  • Dedicated functions for user defined algorithms (i.e. open API)
  • Flexible control of all the necessary parameters

  • R&D, prototyping and design of PHY layer baseband functions and algorithms including proprietary implementations and IPR, where LTE LAB™ shortens the development time
  • Development of RF processing and of higher layers (e.g., MAC) and protocols, where LTE LAB™ serves as a reference model
  • Testing and verification of the developed algorithms or complete equipment elements, where LTE LAB™ provides test and reference signal vectors
  • Education, including specialized technical trainings, as well as university classes, where LTE LAB™ can be used to demonstrate LTE system behaviour and make those events more practical

Tuesday, July 3, 2012

LTE - The Channel quality indicator (CQI)

The Channel quality indicator (CQI) of the definition

  • A combination of modulation scheme and transport block size corresponds to a CQI index
  • Each PDSCH transport block ((modulation scheme + transport block size)  CQI index)
  • Block occupying a group of downlink physical resource blocks  CSI reference resource, received with a transport block error probability (< 0.1).
  •  Highest CQI index between 1 and 15 condition, or CQI index 0 if CQI index 1 does not satisfy the condition,
  • In the frequency domain, the CSI reference resource is defined by the group of downlink physical resource blocks corresponding to the band to which the derived CQI value relates.
  • For periodic CSI reporting, it is an element of the CSI subframe set linked to the periodic CSI report when that UE is configured with CSI subframe sets.
  • An OFDMA frame is divided into K sub channels in the frequency domain and T symbols in the time domain.
  • In each OFDMA frame there are T × K slots and each UE may be allocated one or more such slots according to its application requirements.
  • The slot on the kth subchannel at the tth symbol  denoted as (kth, tth) slot.
  • The CQI of the whole frame is perfectly known at the eNodeB through messages from UEs

Long Term Evolution, Cross layer QoS downlink scheduler, Cross Layer Concept, packet scheduling algorithms

Towards 4g LTE (Long Term Evolution)
  1. LTE - evolution of mobile broadband technology that will deliver users the benefits of faster data speeds and new services by creating a new radio access technology that’s optimized for IP-based traffic and offers operators a simple upgrade path from 3G networks.
  2. LTE is the name of the 4G efforts being undertaken in Europe.
  3. LTE is the result of ongoing work by the 3rd Generation Partnership Project (3GPP), a collaborative group of international standards organizations and mobile-technology companies.
  4. 3GPP(3rd Generation Partnership Project), IEEE and 3GPP2 are three major standard development groups that are in tight competition to satisfy 4th generation requirements.
LTE specifications


1.Support scalable bandwidths -1.4, 3.0, 5.0, 10.0 and 20.0 MHz
2. Peak data rate that scales with system bandwidth
 Downlink (2 Ch MIMO) peak rate of 100 Mbps in 20 MHz channel
 Uplink (single Ch Tx) peak rate of 50 Mbps in 20 MHz channel
3. Supported antenna configurations
Downlink: 4x2, 2x2, 1x2, 1x1
Uplink: 1x2, 1x1
4. Spectrum efficiency
Downlink: 3 to 4 x HSDPA Rel. 6
Uplink: 2 to 3 x HSUPA Rel. 6
5. Latency
C-plane: <50 – 100 ms to establish U-plane
U-plane: <10 ms from UE to server
6. Mobility
Optimized for low speeds (<15 km/hr)
High performance at speeds up to 120 km/hr
Maintain link at speeds up to 350 km/hr
7. Coverage
Full performance up to 5 km
Slight degradation 5 km – 30 km
Operation up to 100 km should not be precluded by standard

PACKET SCHEDULING ALGORITHMS

The packet scheduling algorithms normally classified into two categories:
Physical layer-channel quality information (PHY layer - CQI) based packet scheduling algorithm (Max C/I and RR (Round Robin)) and are designed only for single-service situation
Cross-layer based packet scheduling algorithm (PF (Proportional Fairness), M-LWDF (Modified Largest Weighted Delay First) and EXP-rule) which takes into consideration both PHY-layer CQI as well as data link layer buffer queue information.
They satisfy the principle of multi-service directly
M-LWDF (Modified Largest Weighted Delay First) and EXP-rule, considering time delay for better throughput performance can be achieved, but its packet loss rate performance is still insufficient.
EXP/PF scheduling scheme is to schedule the stream service and best-effort service with EXP-rule and PF-rule respectively.

QoS and Radio Bearer

The Bearer class models the dedicated radio bearer. When a downlink (uplink) flow starts, it activates a dedicated radio bearer between eNodeB and UE (UE and eNodeB) and vice versa
Types of bearer:
(1) Guaranteed bit rate (GBR) which is a permanent bearer and
(2) Non-guaranteed bit rate (non-GBR) which is an IP connectivity bearer.
GBR and non-GBR bearers are associated with different bearer-level QoS parameters which is called QoS Class Identifier (QCI).
The QCI is a scalar denoting a set of transport characteristics (bearer with/without guaranteed bit rate, priority, packet delay budget, packet error loss rate)
QCI used to infer nodes specific parameters that control packet forwarding treatment (e.g., scheduling weights, admission thresholds, queue management thresholds, link-layer protocol configuration, etc.

CROSS LAYERING

A number of (physical and medium access layer) parameters are jointly controlled and functioned with higher layer functions like resource allocation, admission control and routing. Optimization method mainly involving PHY and MAC to manage the system resources adaptively 

 by vinayagam D
Cross Layer Concept in LTE scheduling

The eNodeB creates a list of downlink flows having packets to transmit
MAC queue length and CQI feedbacks are stored for corresponding to each flow.
Scheduling strategy, the chosen metric is computed for each flow
The eNodeB assigns each sub-channel to the users in the flow list that presents the highest metric
For each scheduled flow, the eNodeB computes the size of transport block, i.e., the quota of data that will be transmitted at the MAC layer during the current TTI. 

Cross layer QoS downlink scheduler

Design principle of scheduler
  • Packet belonging to same SDF but to different UEs are queued in different logical queues.
  • Packets in the queue are in the order of arrival time
  • Packet are reordered based on earliest delay deadlines sensitive Real Time SDFs
  • Only HOL packet PHOL  in each queue is consider in each scheduling decision