Towards 4g LTE (Long Term Evolution)
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
- 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.
- LTE is the name of the 4G efforts being undertaken in Europe.
- 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.
- 3GPP(3rd Generation Partnership Project), IEEE and 3GPP2 are three major standard development groups that are in tight competition to satisfy 4th generation requirements.
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
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
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