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Showing posts with label Interference Avoidance. Show all posts
Showing posts with label Interference Avoidance. Show all posts

Sunday, 28 July 2013

New RRC message in Rel-11: In-device coexistence indication

I have blogged about about IDC here and here. If the eNB is interested in knowing if the device is having an interference issue it can ask the UE to send this message in the RRC Conn Reconfiguration message. The UE would send the message if it has interference issues.
Inter-frequency handover is a good solution in case the UE is experiencing interference.

From the Rel-11 whitepaper posted last week here:

To assist the base station in selecting an appropriate solution, all necessary/available assistance information for both time and frequency domain solutions is sent together in the IDC indication. The IDC assistance information contains the list of carrier frequencies suffering from on-going interference and the direction of the interference. Additionally it may also contain time domain patterns or parameters to enable appropriate DRX configuration for time domain solutions on the serving LTE carrier frequency.

Note that the network is in the control of whether or not to activate this interference avoidance mechanism. The InDeviceCoexIndication message from the UE may only be sent if a measurement object for this frequency has been established. This is the case, when the RRCConnectionReconfiguration message from the eNB contains the information element idc-Config. The existence of this message declares that an InDeviceCoexIndication message may be sent. The IDC message indicates which frequencies of which technologies are interfered and gives assistance to possible time domain solutions. These comprise DRX assistance information and a list of IDC subframes, which indicate which HARQ processes E-UTRAN is requested to abstain from using. This information describes only proposals, it is completely up to the network to do the decisions.

Tuesday, 5 February 2013

Interference avoidance for in-device coexistence (IDC)

I posted on this topic couple of years back, so here is a quick update. There is also an article in IEEE Comsoc magazine if you can get hold of it.

Here is the updated 3GPP document



Monday, 10 January 2011

SI on Signalling and procedure for interference avoidance for in-device coexistence

In order to allow users to access various networks and services ubiquitously, an increasing number of UEs are equipped with multiple radio transceivers. For example, a UE may be equipped with LTE, WiFi, and Bluetooth transceivers, and GNSS receivers. One resulting challenge lies in trying to avoid coexistence interference between those collocated radio transceivers. Figure 4-1 below shows an example of coexistence interference.


3GPP initiated a Study Item (SI) in Release-10 timeframe to investigate the effects of the interference due to multiple radios and signalling. This study is detailed in 3GPP TR 36.816 (see link at the end).

Due to extreme proximity of multiple radio transceivers within the same UE, the transmit power of one transmitter may be much higher than the received power level of another receiver. By means of filter technologies and sufficient frequency separation, the transmit signal may not result in significant interference. But for some coexistence scenarios, e.g. different radio technologies within the same UE operating on adjacent frequencies, current state-of-the-art filter technology might not provide sufficient rejection. Therefore, solving the interference problem by single generic RF design may not always be possible and alternative methods needs to be considered. An illustration of such kind of problem is shown in Figure 4-2 above.

The following scenarios were studied:
- LTE coexisting with WiFi
- LTE coexisting with Bluetooth
- LTE Coexisting with GNSS

Based on the analysis in SI, some examples of the problematic coexistence scenarios that need to be further studied are as follows:
- Case 1: LTE Band 40 radio Tx causing interference to ISM radio Rx;
- Case 2: ISM radio Tx causing interference to LTE Band 40 radio Rx;
- Case 3: LTE Band 7 radio Tx causing interference to ISM radio Rx;
- Case 4: LTE Band 7/13/14 radio Tx causing interference to GNSS radio Rx.

In order to facilitate the study, it is also important to identify the usage scenarios that need to be considered. This is because different usage scenarios will lead to different assumption on behaviours of LTE and other technologies radio, which in turn impact on the potential solutions. The following scenarios will be considered:

1a) LTE + BT earphone (VoIP service)
1b) LTE + BT earphone (Multimedia service)
2) LTE + WiFi portable router
3) LTE + WiFi offload
4) LTE + GNSS Receiver

The SI also proposes some ways of reducing the interference and is work in progress at the moment.

Reference: 3GPP TR 36.816 : Study on signalling and procedure for interference avoidance for in-device coexistence; (Release 10).