LTE Power Control ( Downlink power Allocation)

LTE Power Control 

Purpose of Power Control

+ Compensate path loss , including shadow fading and multiple path fading

+ Reduce interference on the edge cell

-LTE systems use the Orthogonal Frequency Division Multiple Access (OFDMA) technique on the downlink and the Single Carrier Frequency Division Multiple Access (SC-FDMA) technique on the uplink. With these techniques, the subcarriers of UEs in a cell are orthogonal. Power control compensates for path loss and shadow fading and counteracts interference between cells. In LTE systems, power control is performed on eNodeBs and UEs. 

DL Power Distribution

- Downlink power control is achieved through fixed power assignment or dynamic power control.

 + Fixed power assignment

Fixed power assignment is applicable to the cell-specific reference signal, synchronization signal, PBCH, PCFICH, and the PDCCH and PDSCH that carry common information of the cell. Users configure fixed power based on channel quality. The configured power must meet the requirements for the downlink coverage of the cell.

+ Dynamic power control

Dynamic power control is applicable to the PHICH and the PDCCH and PDSCH that carry dedicated information sent to UEs. Dynamic power control lowers interference, expands cell capacity, and increases coverage while meeting users' QoS requirements. However, these channels can also support fix power assignment, and in fact, this is our recommendation because the AMC function can also meet the requirement of QoS

Visit our Facebook Page 

Engineering-Academy

Cell Specific RS Power Setting

EPRE: Energy Per Resource Element

The RS power setting is based on EPRE

RS power is the reference power for the other channel

- The cell-specific reference signal is transmitted in all downlink subframes.

 - The signal serves as a basis for downlink channel estimation, which is used for data demodulation.

The power for the cell-specific reference signal is set through the ReferenceSignalPwr parameter, which indicates the Energy Per Resource Element (EPRE) of the cell-specific reference signal.

PB indicator the power ratio between type B symbol and type A symbol, which is specified by 3GPP protocol

RS Power ＝ Total power per channel(dbm) – 10lg(total subcarrier)+10lg(Pb + 1)

Pb determine the RS occupation  of total power, Pb=1 indicate the RS power is 9.4% of total power

Visit our Facebook Page 

Engineering-Academy

Synchronization Signal Power Setting

The synchronization signal is used for cell search and system synchronization. There are two types of synchronization signals, the Primary Synchronization Channel (P-SCH) and the Secondary Synchronization Channel (S-SCH).

The offset of the power for the P-SCH and S-SCH against the power for the cell-specific reference signal is set through the SchPwr parameter.

PowerSCH ＝ ReferenceSignalPwr +SchPwr

PBCH/PCFICH Power Setting

On the PBCH, broadcast messages are sent in each frame. The messages carry the basic system information of the cell, such as the cell bandwidth, antenna configuration, and frame number.

The offset of the power for the PBCH against the power for the cell-specific reference signal is set through the PbchPwr parameter.

The PCFICH carries the number of OFDM symbols used for PDCCH transmission in a subframe. The PCFICH is always mapped to the first OFDM symbol of each subframe.

The power for the PCFICH is set through the PcfichPwr parameter, which indicates an offset of the power for the PCFICH against the power for the cell-specific reference signal.

PowerPBCH ＝ReferenceSignalPwr + PbchPwr

PowerPCFICH ＝ ReferenceSignalPwr + PcfichPwr

PDCCH/PDSCH Power Setting

In the following two status, the power for PDCCH and PDSCH  power is fixed setting

When PDCCH carry scheduling information of common control information (RACH response /paging/SIBs indicator )

When PDSCH carry the common info (RACH response/SIB/paging message)

Dynamic Power Allocation - PHICH

The PHICH occupies very few resources, which means decreasing its transmit power cannot significantly reduce power consumption. In addition, the PHICH carries the ACK/NACK messages for the uplink data, which requires high accuracy. Decreasing the transmit power of the PHICH may reduce accuracy and uplink data rate. Therefore, the dynamic power allocation is not recommended in commercial network. 

Visit our Facebook Page 

Engineering-Academy

Dynamic Power Control - PDCCH

When PDCCH carry the following dedicate info,  power  control should be performed to ensure the receive reliability 

Uplink scheduling information (DCI format 0)

Downlink scheduling information (DCI format 1/1A/1B/2/2A)

PUSCH/PUCCH TPC commands (DCI format 3/3A)

PDSCH Power Presentation

The presentation of  PDCCH power

Regarding power control for the PDSCH, the OFDM symbols on one slot can be classified into two types. Above table shows the OFDM symbol indexes within a slot where the ratio of the EPRE to the EPRE of RS is denoted by ρA or ρB.

Power control for the PDSCH determines the EPREs of different OFDM symbols using ρA and ρB. ρA determines the power offset against the power for the RS when there is no reference signal on the PDSCH, and ρB determines the power offset against the power for the cell-specific reference signal when there is a reference signal on the PDSCH.

PPDSCH_A ＝ ρA + ReferenceSignalPwr

PPDSCH_B ＝ ρB + ReferenceSignalPwr

Visit our Facebook Page 

Engineering-Academy

Carrier Aggregation in LTE

3rd Generation Partnership Project (3GPP) requires LTE-Advanced networks to provide a downlink peak data rate of 1 Gbit/s. However, radio spectrum resources are so scarce that in most cases an operator owns only non-adjacent chunks of the spectrum. Due to the limited bandwidth of a single chunk of the spectrum, the 1 Gbit/s data rate requirement is hard to meet.

To deal with this situation, 3GPP TR 36.913 of Release 10 introduced carrier aggregation (CA) to LTE-Advanced networks, allowing aggregation of contiguous or non-contiguous carriers. CA achieves wider bandwidths (a maximum of 100 MHz) and higher spectral efficiency (especially in spectrum refarming scenarios).

During CA, upper-layer data streams are mapped to individual component carriers (CCs) at the Media Access Control (MAC) layer in LTE-Advanced networks. An eNodeB constructs one (two or more in the case of spatial multiplexing) transport block (TB) in each transmission time interval (TTI) for each CC. Each CC uses its own hybrid automatic repeat request (HARQ) entities and link adaptation mechanism. Therefore, the LTE-Advanced system can inherit single-carrier-based physical layer designs from the LTE system.

why we use the Carrier Aggregation :

Maximized Resource Utilization

A CA-capable UE (referred to as CA UE in this document) can use idle resource blocks (RBs) on up to five CCs to maximize utilization of resources.

Efficient Utilization of Non-contiguous Spectrum Chunks

With CA, an operator's non-contiguous spectrum chunks can be aggregated for efficient utilization.

Better User Experience

With CA enabled, a single UE can reach higher uplink and downlink peak data rates. On a network that serves a number of UEs, CA UEs with activated secondary serving cells (SCells) can use idle resources in their SCells and achieve increased throughput if the network is not overloaded.

Introduction of carrier aggregation influences mainly MAC and the physical layer protocol, but also some new RRC messages are introduced. In order to keep R8/R9 compatibility the protocol changes will be kept to a minimum. Basically each component carrier is treated as an R8 carrier. However some changes are required, such as new RRC messages in order to handle SCC, and MAC must be able to handle scheduling on a number of CCs. Major changes on the physical layer are for example that signaling information about scheduling on CCs must be provided DL as well as HARQ ACK/NACK per CC must be delivered UL and DL,as shown in the below figure:

The uplink and downlink air-interface protocol stack with CA enabled has the following characteristics:

    A single radio bearer has only one Packet Data Convergence Protocol (PDCP) entity and one Radio Link Control (RLC) entity. In addition, the number of CCs at the physical layer is invisible to the RLC layer.

    User-plane data scheduling at the MAC layer is performed separately for individual CCs.

    Each CC has an independent set of transport channels and separate HARQ entities and retransmission processes.

When carrier aggregation is used there are a number of serving cells, one for each component carrier. The coverage of the serving cells may differ, for example due to that CCs on different frequency bands will experience different pathloss, see figure 3. The RRC connection is only handled by one cell, the Primary serving cell, served by the Primary component carrier (DL and UL PCC). It is also on the DL PCC that the UE receives NAS information, such as security parameters. In idle mode the UE listens to system information on the DL PCC. On the UL PCC PUCCH is sent. The other component carriers are all referred to as Secondary component carriers (DL and UL SCC), serving the Secondary serving cells, see figure 3. The SCCs are added and removed as required, while the PCC is only changed at handover. 

there are a lot of scenarios that we can use the CA in it:

1- intra-eNodeB CO Coverage 

  2- intra-eNodeB different coverage carriers 

3- Intra-eNodeB carriers (one for macro coverage; another for edge coverage)

4-Intra-eNodeB carriers (one provided by the site; another provided by RRHs)

5-Intra-eNodeB carriers (one provided only by the site; another provided by the site and a repeater)

VAMOS (Voice services over Adaptive Multi-user channels on One Slot) IN GSM part1

VAMOS

BY engineer :abdallah Saleh 

VAMOS stands for Voice services over Adaptive Multi-user channels on One Slot. The idea here is to increase the voice calls capacity supported by GSM network. It is possible to use one time slot for four voice calls/services
The feature VAMOS is specified in 3GPP release 9.
VAMOS assign the same GSM physical channel (ARFCN-TDMA frame number-Time Slot) into two users simultaneously.
The GSM channel could be:
-Full Rate Channel
-Two Half Rate Channels
-Two VAMOS Full Rate Channels
-Four VAMOS Half Rate Channels
-One Half Rate Channel and Two VAMOS Half Rate Channels
-One VAMOS Full Rate Channel and Two VAMOS Half Rate Channels

VAMOS Advantages:

1-Doubling of voice calls per transceiver 

Increased call capacity per transceiver gives operators an efficient means to handle voice traffic growth in their networks without adding more TRXs.

Avoiding additional TRX’s results in savings in BTS HW investments, energy consumption and BTS foot print.

2-Free up capacity for EDGE data services

VAMOS reduces the number of time slots needed for voice services. This allows more time slots to be allocated for EDGE services.

Note: EDGE can carry a bandwidth up to 236.8 Kbit/s for 4 timeslots (theoretical maximum is 473.6 Kbit/s for 8 timeslots) in packet mode.

3-Free up spectrum for new technologies

For example UMTS900 (reframing 25 GSM 200 KHz frequency channel into 5 MHz UMTS Carrier) or LTE which allow for flexible operations in different spectrum bands.

VAMOS Disadvantage:

1-The parallel signal transmission of the two multiplexed users causes interference for one another, affecting speech quality if not properly controlled.

2-Call Drop Rate increased due to multiplexing of different MSs types.

facebook page 

                                     Engineering-Academy

How VAMOS can differentiate between two users?

VAMOS transmits the combination of two signals at the same time over the same channel, each with a different orthogonal TSC’s (Training Sequence Code). 

Each of the two MSs that receive the data stream at the same time use their knowledge of their individual TSC to reconstruct their own part of the signal, effectively filtering away the second data stream as noise. 

Up-Link Operation:

Transmitter (MS): use the existing GMSK modulation scheme. In other words, no new transmitter elements are required in mobile devices. 

Receiver (BTS): different receiver algorithms may be used, that is Space Time Interference Rejection Combining (STIRC), Successive Interference Cancellation (SIC) or Joint Detection (JD) to receive both orthogonal sub-channels distinguished by their individual training sequences. Another option is to use two independent GMSK receivers for each sub-channel.

Down-Link Operation:

Transmitter (BTS): use AQPSK modulation technique to be able to transmit two calls at the same time.

Receiver (MS): use 3GPP Downlink Advanced Receiver Performance (DARP) which is also known as Single Antenna Interference Cancellation (SAIC) algorithm to correctly demodulate downlink Signal.

Training Sequences 

The training sequence code (TSC) or Channel Sounding Bits is a known 26-bit pattern placed in the middle of normal burst. TSC has eight fixed formats, which are represented by TSC ranged 0:7 respectively. The eight sequences are stored in all MS receivers to be used for Bit Synchronization and for Channel Estimation.

Because of TSC at the middle of time slot it also called Midamble. By having TSC there, the chances are better that the channel is not too different when it affects the training sequence compared to when the information bits were affected. If TSC was at the start of a burst, the channel might have changed by the end of the burst, and the same thing if it was at the end.

If MS have read SCH, it must get the TSC (Training Sequent Code) to correctly read the information on the downlink common signaling channel. TSC number is linked to the Base Station Color Code (BCC) of the cell. So one of the functions of BSIC is to inform MS of the TSC adopted by the common signaling channel of the cell.

to understand the VAMOS read other parts 

Part 1

part 2

Part 3

facebook page 

                                     Engineering-Academy

3G Optimization Paging Reception

The purpose of the paging procedure is as follows:

-The core network (CN) originates the paging procedure to inform selected UEs of service requests and to trigger reading of updated UTRAN system information.
-The UTRAN originates the paging procedure to trigger state transitions from URA_PCH to CELL_FACH or idle mode for selected UEs.

1-Paging Types 

Paging UE in Idle, CELL_PCH, URA_PCH State (Type 1)

+When an UE is in idle, CELL_PCH, or URA_PCH state, UTRAN sends a paging message to the UE through the PCCH.

Paging type 1 procedure is used to transmit paging information to the selected UEs in idle mode, CELL_PCH or URA_PCH state using the PCCH. With this feature, upper layers in the network can:

-Trigger UE establishing an RRC signaling connection.

-Trigger CELL UPDATE procedure of UE in CELL_PCH or URA_PCH state.

-Trigger reading of updated system broadcast of UE in idle mode, CELL_PCH or URA_PCH state.

-Trigger releasing signaling connection of UE in CELL_PCH or URA_PCH state.

+When the CN sends data to UEs in CELL_PCH or URA_PCH state, the UTRAN shall repeat the paging process five times in case of a paging failure towards a UE for some reasons (For example, the UE has moved out of the UTRAN and transferred to an inter-RAT network.). If the UTRAN still fails to page the UE, the UTRAN considers that the paging towards the UE fails and releases the RRC connection with the UE.

Paging UE in CELL_FACH, CELL_DCH State (Type 2)

The network can control the UE in CELL_FACH or CELL_DCH state which has DCCH with paging type 2 procedures. In paging type 2, UTRAN sends a paging message to the UE in CELL_FACH or CELL_DCH state through the DCCH or FACH.

 Reception Technology

+To reduce power consumption, the UE can read the information from the PICH only at a particular time. This is known as the Discontinuous Reception (DRX) technology. The interval between two consecutive receiving occasion is called DRX cycle.

+For Frequency Division Duplex (FDD), the DRX cycle length shall be 2k frames, where k is an integer and is determined by the following three parameters:

-CN domain specific DRX cycle length for CS

-CN domain specific DRX cycle length for PS

-UTRAN DRX cycle length coefficient

The description of the parameters is as follows:

-CN domain specific DRX cycle lengths

facebook page 

Engineering-Academy

-The UE may be attached to different CN domains with different CN domain specific DRX cycle lengths. The UE shall store these lengths for all CN domains where the UE is attached and shall use the shortest one.

-UTRAN DRX cycle length

+For a UE in idle mode, the DRX cycle length equals the shortest value of the stored DRX cycle length for the CN domains where the UE is attached, with no signaling connection established.

+For a UE in CELL_PCH state or URA_PCH state, the DRX cycle length equals the shortest value of the following lengths:

-UTRAN DRX cycle length

-Any of the stored DRX cycle length for the CN domains where the UE is attached, with no signaling connection established

If you set a great DRX cycle length coefficient, the period for UE detect paging information will be long; therefore, the UE can reduce the power consumption, but the delay for responding to a paging will be long.

why we Use Channel Quality Indicator (CQI) in UMTS not only the ECNO??

CQI report 

UE sends a Channel Quality Indicator (CQI) on the uplink (HS-DPCCH)

CQI

-Estimates the number of bits that can be transmitted to the UE using a certain assumed HS-PDSCH -power with a block error rate of 10%
-UE receiver performance
Good UE receiver can report that it can receive more bits than a Bad UE receiver implementation for the same channel conditions.

PCPICH_RX	Received power of the P-CPICH
Г	Measurement Power Offset MPO
	Cell level parameter hsMeasurementPowerOffset
∆	Reference power adjustment
	Given by Table 7A, 7B, 7C, 7D, 7E, 7F or 7G depending on the UE category.

Physical layer procedures (FDD)

CQI algorithm indicates 

-Transport block size

-Number of HS-PDSCH codes

-Modulation Type

-HS-PDSCH Power

HSDPA Scheduler algorithm indicates

 -Which UE to transmit to in the TTI, 

-Available HS-PDSCH transmission power, Available number of HS-PDSCH codes. 

-It does not indicate how much data to transmit.

CAT6
CQI Value	Transport Block Size	Number of HS-PDSCH	Modulation	Reference Power Adjustment
1	137	1	QPSK	0
2	173	1	QPSK	0
3	233	1	QPSK	0
4	317	1	QPSK	0
5	377	1	QPSK	0
6	461	1	QPSK	0
7	650	2	QPSK	0
8	792	2	QPSK	0
9	931	2	QPSK	0
10	1262	3	QPSK	0
11	1483	3	QPSK	0
12	1742	3	QPSK	0
13	2279	4	QPSK	0
14	2583	4	QPSK	0
15	3319	5	QPSK	0
16	3565	5	16-QAM	0
17	4189	5	16-QAM	0
18	4664	5	16-QAM	0
19	5287	5	16-QAM	0
20	5887	5	16-QAM	0
21	6554	5	16-QAM	0
22	7168	5	16-QAM	0
23	7168	5	16-QAM	-1
24	7168	5	16-QAM	-2
25	7168	5	16-QAM	-3
26	7168	5	16-QAM	-4
27	7168	5	16-QAM	-5
28	7168	5	16-QAM	-6
29	7168	5	16-QAM	-7
30	7168	5	16-QAM	-8

Why CQI?

Back to  Basics:

PN codes (distinguish each Base Station)

-Not orthogonal

-High cross correlation properties

-PN1 * PN2  ≠ 0 (mini. output)  

Channelization Codes (distinguish data channels Coming from each Base Station)

-Orthogonal Codes

-OC1 * OC2 = 0

-Ec/No for most of us is quality measurement metric. 

-It gives us how good or bad the link quality is.

-However by definition it is confusing

RSCP

-Received signal code power

-Received power level of pilot channel of a one cell (dBm/mW)

-Using RSCP we can compare different cells

-Using RSCP handover and cell reselection decisions can be taken

RSSI

-Signal power over the complete 5MHZ carrier which include all components received 

-Signal from the current cell and neighboring cells on the same frequency

-Theoretically in an isolated cell having only CPICH power with no other channels  

RSSI ≈ CPICH power 

-RSSI will change if the carrier use the DCH or the common channels

CPICH  Ec/No

-Pilot channel quality ,energy per chip over total received power spectral density

Ec/No= RSCP/RSSI

-The Better this value the better the signal can be distinguished from the over all nosie

-Always negative 

-Using Ec/No we can compare different cells

-Using Ec/No handover and cell reselection decisions can be taken

Visit our Facebook Page 

Engineering-Academy

Noise power spectral density 

-Interfering power  

-Non interfering power 

-Thermal noise

-Test bed being served by single cell

Ec/No of UE is 

Measure of PCPICH =RSCP

Measure of total wide band power =RSSI

Assume that UE is in Test bed being served by single cell`

-Cell MAXTXPOWER  20 watt (43 dBm)

-Assuming that 10 % of the cell power is dedicated for CPICH 2 watt (33 dBm)

-If you have no DCH or HS channels 

-Ec/No= 10 log (CPICH Power/Total transmitted power)

-Ec/No=10 log (2w/2w)= 10 log 1 = 0

Assume that you start HS session

-Ec/No= 10 log (CPICH Power/Total transmitted power)

-Ec/No=10 log (2w/20w)= -10 dB (Poor value)

-Ec/No will always give a false value for an HSDPA user

CQI Adjustment

Deviating CQI reports lead to faulty decisions

-CQI accuracy will continue to vary depend on :

-UE model 

-UE vendor

Deviating CQI

-UE that consistently overestimates the channel quality

+Scheduled too often, at the price of other users. 

+Experience a block error rate that is higher than the target 10%, with more retransmissions and reduced system throughput and increased service delay

-UE instead underestimates the channel quality

 +Scheduled too seldom. 

+Experience a Block error rate will be lower than 10%, which will lead to lower transmitted data rates than possible and hence reduced system throughput.

In both cases, both system throughput and end-user experience of the service is negatively impacted.

To avoid the negative system impact due to inaccurate CQI reports, 

-CQI adjustment algorithm 

+RBS works on the ACKs and NACKs received from the UE to determine if the UE is overestimating or underestimating the channel quality. 

+The algorithm make every effort to achieve a block error rate of 10%

-The output from the adjustment algorithm is CQIadjusted, 

-The CQI adjustment algorithm is an optional feature and can be enabled on cell level through parameter cqiAdjustmentOn

Visit our Facebook Page 

Engineering-Academy