3GPP LTE Channels and MAC Layer

Contents:-

• LTE MAC Layer Functions
• MAC in the LTE Protocol Stack
• LTE Channel Architecture

• Downlink PDCP, RLC and MAC Sublayer Organization
• Uplink PDCP, RLC and MAC Sublayer Organization
• LTE Downlink Channels

• LTE Uplink Channels
• 
• Random Access Procedure
• UL/DL-SCH data transfer

Download from here.....

Alcatel-Lucent Announces Loss and Plans to Cut Down 5,000 Jobs

Mobile equipment major Alcatel-Lucent has decided to slash 5,000 jobs.


The telecom equipment maker will restructure unprofitable markets as part of a program to lower costs by 1.25 billion euros ($1.52 billion) by the end of next year.


Alcatel-Lucent will miss its 2012 profit margin target and pre-announced an adjusted operating loss of 40 million euros on sales above 3.5 billion in the second quarter.


The job cuts will affect 6.4 percent of Alcatel-Lucent's 78,000 employees. The group will also seek to get rid of unprofitable services contracts in which it manages networks for operators, squeeze more money out of its patent portfolio, and exit or restructure in countries where it is weak.


Alcatel-Lucent also gave a new annual profit target of posting a second-half adjusted operating margin better than the first half when it stood at minus 3.7 percent. It confirmed its prior target of aiming for a strong positive net cash position at the end of 2012.


Recently, Nokia and RIM announced their plans to cut jobs.


Alcatel-Lucent said sales in its wireless and optic divisions had a double-digit decline in revenue because of moderate spending from service providers. Sales in its software, services and solution segment also declined, and the services business was almost flat, it added.


Revenue in North-America, Europe and the Asia Pacific region witnessed a double-digit decline, the company said, adding that the decline in Asia was mainly driven byChina, where sales fell by 21 percent.



Competitive pricing was one of the main reasons that eroded profitability, the company said. Overall revenue was €3.5 billion, down 7.1 percent year-over-year.
"These times demand firm actions," said Alcatel-Lucent's CEO Ben Verwaayen in a statement. Besides cutting 6.6 percent of its total of 76,000 employees the company also plans to exit and restructure unprofitable markets and is planning to manage its patent portfolio as an independent profit center, it said.

Huawei surpasses Ericsson as world's largest telecom equipment vendor

Huawei is set to retain top telecom equipment vendor position in coming quarters, thanks to its growing revenue from enterprise and mobile phone businesses.


Its main rivals - Ericsson and Nokia Siemens - do not have this big opportunity to compete with the Chinese telecom equipment maker. 



Chinese telecoms giant Huawei Technologies on Tuesday reported a 5.1 percent rise in sales to 102.7 billion yuan (US$16.1 billion) for first-half 2012, ended Jun. 30, which surpassed Ericsson's 106.3 billion kronor (US$15.25 billion) over the same period.



Since 2011, the slowdown in the global market have seen telecom operators worldwide reporting lower income and profits, resulting in even greater competition between telecom equipment manufacturers.


"[Huawei] continues to maintain robust growth momentum, although the global economic situation and telecom equipment market remains a significant challenge," said the company.


The Chinese telco player was "relatively optimistic" about the operating performance and profitability for the remainder of 2012, said its CFO Meng Wanzhou.


According to Ying Weimin, President of Huawei GSM&UMTS&LTE Network, Huawei helped Deutsche Telekom, Telefonica, Telenor, TeliaSonera, and Vodafone launch their LTE services commercially.

A document on SC-FDMA from Agilent

Contents:-

• LTE objectives and timing
• OFDM:The choice of nect-generation wireless
• Assessing the advantages and disadvantages of OFDM
• Introducing SC-FDMA
• Comparing SC-FDMA and OFDM
• Multipath resistance with short data symbols?
• Examining real SC-FDMA signal 

Download from here......

MIMO in LTE Operation and Measurement

This application note is written for people who need an understanding of Multiple Input Multiple Output (MIMO) radio operation as it applies to Long Term Evolution (LTE). MIMO (otherwise known as spatial multiplexing) is one of several multiple antenna techniques that are being implemented in LTE; however, this application note will primarily focus on MIMO implementations.


Contents:-

• Inputs and Outputs
• Single User and Multi-User MIMO
• Single and Multiple User MIMO in the Uplink
• LTE Transmitter and Receiver Design and Test
• Receiver Design and Test
• Transmitter Design and Test
• A Systematic Approach to Verifying Transmitter Quality

Download from here...

Long Term Evolution (LTE) Video Presentations

Here you can find some of excellent video trainings off LTE which covers following topics.


Contents:- 



1. LTE Introduction

• Motivations for LTE
• LTE market and background
• Requirements
• Evolution path to LTE

2. LTE Parameters and Downlink Modulation

• LTE parameters and frequency bands
• What is OFDMA?
• OFDMA multiple access and downlink frame structure
• OFDMA transmit and receive chains

3. OFDMA and Downlink Frame Structure Details

• Downlink OFDMA time-frequency multiplexing
• LTE Spectrum Flexibility and Bandwidth
• FDD downlink frame structure detailed
• TDD frame structure

4. SC-FDMA and LTE Uplink

• Introduction to SC-FDMA and uplink frame structure
• Uplink SC-FDMA tranmsit and receive chains
• Peak to Average Power Ratio (PAPR) comparison with SC-FDMA and OFDMA

5. Network and Protocol Architecture

• LTE/SAE network architecture
• EPC -Evolved Packet Core
• Base Station control plane and user plane protocol stacks
• EPC protocol stacks

6. Channel Mapping and UE Categories

• Logical and transport channel mapping in downlink and uplink
• LTE UE Categories

7. Initial Cell Search and Cell Selection

• Downlink physical channels and signals
• Cell Search and Selection in LTE
• Primary synchronization signal
• Secondary synchronization signal
• Reference signals

8. System Information

• Downlink reference signal details
• Master Information Block on PBCH
• System Information on DL-SCH

9. Random Access Procedure and EPS Bearer Setup

• Random access preamble transmission to eNodeB
• Random access response from eNodeB
• Resource allocation and contention resolution
• Signaling on PDCCH
• Hybrid ARQ
• RRC Connection Setup and EPS Bearer Setup

10. Uplink Channels and Signals

• Uplink physical channels and signals
• PU-SCH: Physical Uplink Shared Channel
• Uplink assignment signaling on PDCCH
• Uplink frequency hopping
• PUCCH

11. LTE mobility and MIMO Introduction

• Intra MME Handover over the X2 interface
• RRC States
• MIMO Basics
• Transmit diversity
• Spatial multiplexing
• Beamforming

12. Downlink and Uplink MIMO in LTE

• Downlink MIMO modes
• Transmit diversity
• Spatial multiplexing
• Cyclic delay diversity
• Beam forming
• Spatial multiplexing downlink transmitter chain
• Code book based precoding
• Uplink MIMO
• Uplink transmit antenna selection
• Multi-user MIMO

13. eNodeB and UE RF Performance Requirements

• eNodeB modulation quality measurements
• eNodeB performance requirements
• UE performance requirements

14. UE Certification and Field Trials

• LTE terminal testing stages
• LTE terminal certification
• LTE field trial scenarios

View from here.....

How Random Access procedure works in LTE?

The RACH procedure in LTE is used for four cases: 

• Initial access from disconnected state (RRC_IDLE) or radio failure .
• Handover requiring random access procedure.
• DL or UL data arrival during RRC_CONNECTED after UL PHY has lost synchronization (possibly due to power save operation).
• UL data arrival when are no dedicated scheduling request (PUCCH) channels available.

Timing is critical because the UE can move different distances from the base station, and LTE requires microsecond level precision; the speed-of-light propagation delay alone can cause enough change to cause a collision or a timing problem if it is not maintained. 

There are two forms of the RACH procedure: Contention-based, which can apply to all four events above, and noncontention based, which applies to only handover and DL data arrival. The difference is whether or not there is a possibility for failure using an overlapping RACH preamble.

Read more from here.....

what is use of cyclic prefix in LTE OFDM signals?

To limit the influence of ICI on OFDM systems completely by hardware we would have to have transmitters and receivers with under 0.1ppm frequency stability. This would drastically increase the cost and complexity of hardware.Thus quite a big part of the OFDM software in the receiver deals with frequency correction using the cyclic prefix, but also reference or pilot signals sent with the signal.



The cyclic prefix (CP) consists of the last part of the following symbol. The size of the cyclic prefix field depends on the system and can even vary within one system. Cyclic prefixes are used by all modern OFDM systems and their sizes range from 1/4 to 1/32 of a symbol period. Most receiver structure use the cyclic prefix to make an initial estimation of time and frequency synchronization.


Read more from here.........

What is special sub frame in LTE?

As the single frequency block is shared in time domain between UL and DL the transmission in TDD is not continuous. All UL transmission need to be on hold while any downlink resource it is used and the other way around. 


Switching between transmission directions has a small hardware delay (for both UE and NodeB) and needs to be compensated. To control the switching between the UL and DL a guard period GP is allocated which compensates for the maximum propagation delay of interfering components.


Description of the switching mechanism:
In LTE TDD there is maximally one UL->DL and one DL->UL transition per 5ms period (half frame)
UL-> DL transition
Is done for all intra-cell UEs by the process of time alignment. The NodeB instructs each UE to use a specific time offset so that all UEs signals are aligned when they arrive at Node-B. So UL is synchronous very similar to FDD (intra cell case only!)



As shown in above figure there are 7 frame configurations, according to different DL/UL partition.
1. Downlink / Uplink ratio can vary from 1/3 (Frame configuration = 0) to 8/1 (Frame configuration = 1), depending on the service requirements of the carrier
2. Frame always starts with a downlink subframe, used for advertising the frame descriptor, PCFICH and PDCCH. UE hence learns the frame structure in this subframe.
3. 3rd frame is always used for uplink
4. When switching from downlink to uplink, there is need for a special switching subframe. No special subframe is used when switching from uplink to downlink.


Read more from here......

What are the benefits and drawbacks of an OFDMA?

OFDM/OFDMA has several benefits over other transmission schemes:



1. High spectral efficiency: due to the orthogonality between subcarriers it is possible to pack them closely together (15kHz subcarrier spacing)
2. Little interference between subcarriers due to the IFFT/FFT processing (Interference can be introduced by frequency offsets generated by either Doppler or Local Oscillator frequency innacuracies).
3. Robustness in multi-path environments thanks to the cyclic prefix as mentioned before.
4. Straightforward support of the operation in different spectrum allocations with different bandwidths just by varying the number of OFDM subcarriers used for transmission.
5.Simpler receiver design to support high data rate communications. Detecting a rectangular pulse with cyclic prefix requires less hardware. Free capacity can be used then to implement other performance optimization techniques.
6. Easy MIMO techniques implementation


Drawbacks of OFDMA:-


1. The main disadvantage of OFDM/OFDMA is that the signal has a relatively large peak-to-average power ratio (PAPR). This is due to the nature of OFMA where modulated symbols are transmitted in parallel, each one containing a part of the transmission. The power at a certain point in time is the sum of the powers of all the transmitted symbols for a certain connection, which explains that the differences between peak and average powers can be high.

2. This issue reduces the power efficiency of the RF amplifier. Expensive transmission amplifiers are needed, especially on the mobile side, in order to work on a wide range of powers; otherwise the non-linear amplification reduces the orthogonality of the OFDM signal. This is a reason why OFDMA is not optimal for use with mobile or battery-power devices.

3. Other issue of OFDM/OFDMA systems is that tight spacing of subcarriers may lead to loss of orthogonality due to frequency errors. Doppler may cause inter carrier interference (ICI) and the consequent lost of orthogonality. To cope with the problems caused by close subcarrier spacing, LTE has adopted 15 kHz spacing (mobile WiMAX uses 10KHz spacing).