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that is vital for the operation of both downlink carriers (HS-DPCCH) is always only carried on the primary<br />
uplink carrier.<br />
B.1.4 TRANSMIT DIVERSITY EXTENSION FOR NON‐MIMO UES<br />
The 2X2 MIMO operation for HSDPA specified in Rel-7 allows transmission of up to two parallel data<br />
streams to a MIMO UE over a single carrier. If and when the HSDPA scheduler in the base station<br />
decides to only transmit a single stream to the UE for any reason (e.g. because the radio channel<br />
temporarily does not support dual-stream transmission), the two transmit antennas in the base station will<br />
be used to improve the downlink coverage by single-stream transmission using BF.<br />
As MIMO is being deployed in more and more networks, single-stream transmission using BF also<br />
towards non-MIMO UEs that reside in MIMO cells becomes an increasingly attractive possibility.<br />
Therefore, this option has been introduced in Rel-9, reusing L1/L2 solutions from Rel-7 MIMO to as large<br />
extent as possible. This is referred to as “single-stream MIMO” or “MIMO with single-stream restriction.”<br />
For a multi-carrier HSDPA user, the usage of single-stream MIMO can be configured independently per<br />
carrier.<br />
B.2 LTE ENHANCEMENTS<br />
B.2.1 IMS EMERGENCY OVER EPS<br />
Emergency bearer services are provided to support IMS emergency sessions. A main differentiator of an<br />
IMS emergency session is that emergency service is not a subscription service and therefore, when the<br />
UE has roamed out of its home network, emergency service is provided in the roamed-to network and not<br />
the home network.<br />
Emergency bearer services are functionalities provided by the serving network when the network is<br />
configured to support emergency services. Emergency bearer services can be supplied to validated UEs<br />
and depending on local regulation, to UEs that are in limited service state and otherwise not allowed on<br />
the network. Receiving emergency services in limited service state does not require a subscription.<br />
Depending on local regulation and an operator's policy, the MME may allow or reject an emergency<br />
request for network access for UEs in limited service state. To support local regulation, four different<br />
behaviors of emergency bearer support have been identified as follows:<br />
1. Valid UEs only. No limited service state UEs are supported in the network. Only normal UEs that<br />
have a valid subscription, and are authenticated and authorized for PS service in the attached<br />
location are allowed.<br />
2. Only UEs that are authenticated are allowed. These UEs must have a valid IMSI. These UEs<br />
are authenticated and may be in limited service state due to being in a location that they are<br />
restricted from regular service. A UE that cannot be authenticated will be rejected.<br />
3. IMSI required, authentication optional. These UEs must have an IMSI. Even if authentication<br />
fails, the UE is granted access and the unauthenticated IMSI retained in the network for recording<br />
purposes.<br />
4. All UEs are allowed. Along with authenticated UEs, this includes UEs with an IMSI that cannot<br />
be authenticated and UEs with only an IMEI. If an unauthenticated IMSI is provided by the UE,<br />
www.4gamericas.org February 2011 Page 113
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