How QoS is managed in LTE/EPS system

eNB manage traffic QoS requirement on two aspectsOn the radio interfaceOn the transport (backhaul)

A. QoS mechanisms in the radio part
1) Radio bearer control

QoS functionality in the RBC is to dynamically monitors the quality of service status of ongoing RBs based on the interaction with the MAC Scheduler. When quality of service requirements for an ongoing RBs are not fulfilled, QoS invokes the RBC function to release or to reconfigure the corresponding radio bearer.

2) Scheduling

MAC scheduler plays an important role to achieve required QoS for each radio bearer.Scheduling priority is a continuous function of QCI, GBR, delay budget, etc. For example, below formula can be used when calculating scheduling metric:M = R * Mqos * Mqci / (T^Alpha)

R is the expected/wanted bit rate

Mqos is the QoS metric

Mcqi is the QCI metric

T is the actual bit rate in the last scheduling period

Alpha is a fairness factor, Alpha = 0 means the system doesn't care what has been achieved, scheduling metric is only determined by the demand, therefore it is unfair among users;

Alpha > 1 means the system gives more weight to each UE's the performance, finding fairness among users.

3) Admission control

4) Congestion control5） ICICBasically, like AC and CC, ICIC function module just provide constraints to scheduling function.

B. QoS mechanisms in the transport

1) DiffServ uses the 6-bit Differentiated Services Code Point (DSCP) field in the header of IP packets for packet classification purposes. eNB maps QCI against DSCP so that the IP packets are marked with corresponding QoS requirements.

2) Mapping DSCP with P-bit in VLAN. In case of VLAN is supported, QoS priority is preserved as P-bit (7 bit) within a VLAN ID.

Key technologies to improve LTE coverage and link quality

What are the key technologies being used in LTE to improve network coverage and link quality?
My tentative answer can be found below:

• Adaptive modulation and coding (AMC)

On the downlink, to optimize system capacity and coverage, eNodeB will try to match the information data rate for each user to the variations of its received signal quality. UE can be configured to report CQIs (Channel Quality Indicator), RI (Rank Indicator) and PMI to assist eNodeB in selecting an appropriate transmission parameters such as MCS index, number of MIMO ranks and pre-coding parameter for the downlink transmissions. On the uplink, eNodeB can dynamically choose MCS value to send in the DCI (Downlink control information), to specify uplink MCS to be used by the UE, according to CQI values that UE reports. ·

• Rank and MIMO scheme adaption

Rank adaption modifies the Tx layers based on UE feedback. MIMO scheme selection takes measurement statistics for PUCCH evaluated at eNB so that to select an appropriate MIMO scheme.

- Tx Diversity and 2x2 SU-MIMO transimission schemes, are dynamically updated per UE according to the channel conditions an UE experienced.

- Close loop MIMO is selected for low speed users, while for high speed users Tx diversity or OL MIMO is selected depend on UE feedback, e.g. CQIs.

• Frequency hopping

Type 1 (inter-TTI) or type 2 (Intra/Inter-TTI) frequency hopping in LR3.0. Frequency hopping is useful to combat frequency selective fading and minimize inter-cell interference.

• TTI bundling

For VoIP or other read time traffic, TTI bundling can be used to improve cell edge performance.

• SIC

A successive interference cancellation (SIC) receiver can detect and decode the CWs of the data streams in such a way that if the CW of one data stream is successfully decoded (indicated by a cyclic redundancy check (CRC) code), the decoded data is then reencoded, remodulated, etc., and cancelled from the originally received signal. Thus, interference is reduced for the remaining data streams.

network sharing

Driver:

The operators are facing unprecedented challenges in particular during these recession days.

- decreased in voice revenues

- maintaining profit

The solution would naturally be on two aspects:

- generating new revenue by introducing new services, such as mobile broadband, mobile TV, SDP (iTunes, Nokia OVI store), etc

- cost reduction

RAN sharing is one solution leading to cost reduction, other options such as complete network outsourcing,

network O&M outsourcing are also worth considering, depends on operators' specific situation.

Solution:

Site sharing installs two or more operators' network equipments (mostly RAN) on the same site/tower. This is the simplest way, no much requirement to eNB (as eNB are still seperate). Backhaul traffic aggregation plays the most important role in cost saving in this case.

Real RAN sharing shares the same eNB with two or more operators. This requires some specific features within eNB to enable the sharing.

- multi- PLMN-id broadcast. The eNB can be configured to broadcast more than one set of PLMN-ids and more than one set of SIBs - as if two networks co-exist.

- VLAN. eNB needs to support VLAN so that each operator use one or more VLANs

- multiple IP address. The eNB should be addressed by different IP address on different operator's network

- resource allocation/balancing. The eNB should support configuration that its resource (HW, radio, etc) can be divided between the operators so that the system is not overwhelmed by a single operator's traffic.

- independent QoS management. However, the eNB should treat each operators traffic independently so that each operator has its own scheduling, RRM, QoS managment policy.

Architecture

Two types of RAN sharing architecture is defined.

- The first is called GWCN, where both GW and RAN are shared

- The second is called MOCN, where eNB connects to different MME/GW from each operator.

Most likely the second option will be more popular.