Difference between revisions of "GSOC2010MACPHYforLTE"
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''Details about the ideal control channel''
''Details about the ideal control channel''
== Schedule ==
== Schedule ==
Revision as of 14:52, 15 May 2010
Long Term Evolution represents an emerging and promising technology for providing a broadband ubiquitous Internet access. For this reason, several research groups are working on LTE to provide newer and innovative solutions, able to optimize its performance.
Unfortunately, no ns-3 modules have been developed to simulate LTE networks. This project consist of a development of a framework to simulate LTE networks on ns-3, composed by both PHY and MAC models.
The development of the LTE module for ns-3 is composed by two consecutive steps. The first one is the development of the PHY model and the second one is the development of the MAC mode. The module will be implemented into the src/device/lte folder.
Regarding the PHY model, starting from the Nicola's spectrum framework proposed in  will be implemented the following features: (i) a new PHY spectrum for the LTE, (ii) the LTE spectrum model, and (iii) the LTE propagation Loss model. For the PHY model, a couple of half-duplex PHY will be defined, one for the downlink and one for the uplink. In this way it is possible to provide the support for the FDD channel access. The LTE spectrum model will take into the account that the whole LTE bandwidth (20Mhz @ 2GHz) is divided into 100 sub channel of 180 KHz. The the LTE propagation Loss model will be used to obtain the received spectrum spectrum. According to , four models (shadowing, multipath, path loss, and penetration loss) will be chained into a single model. For wath concern the spactrum channel, it will be used the SingleModelSpectrum Channel proposed with the spectrum framework.
Regarding the MAC model, the LTE network devices (eNB and UE) will be implemented. For each device will be defined the following elements: (i) the LTE Spectrum Physical, (ii) the AMC Module, (iii) the Bearer Manager. For the eNB will be defined also the following elements: (i) Downlink Scheduler, (ii) Frame Manager, and (iii) list of registered UE. A bearer class will be implemented to manage one LTE flow between eNB and UE. For each Bearer a MAC queue will be also developed.
The framework is designed to simulate only data transmissions. For the transmission of control messages (such as CQI feedback, PDCCH, etc..) will be used an ideal control channel).
Details about the PHY model:
The LTE PHY model is created starting from the Spectrum Framework proposed in . In particular, to define a LTE spectrum model mean specify the LTESpectrumModel, the LTESpectrumPHY, and the LTESpectrumPropagationLossModel.
The LTESpectrumModel is created in order to define a set of LTE sub channels (100 for 20MHz of bandwidth).
The LTESpectrumPHY represents the physical layer of a LTE device and it is responsible of the transmission and the reception of packets belonging to the device of caming from to the channel. Regarding the LTE channel, it will be used the already implemented SingleModelSpectrumChannel.
The LTESpectrumPropagationLossModel is created in order to compute the power of the received signal. The power loss due to the channel is computed considering at the same time four different models (shadowing, multipath, penetration loss and path loss). As proposed in , these models are decribed in the following:
- Pathloss: PL = 128.1 + (37.6 * log10 (R)), where R is the distance between the UE and the eNB in Km.
- Multipath: Jakes model
- PenetrationLoss: 10 dB
- Shadowing: log-normal distribution (mean=0dB, standard deviation=8dB)
Every time that the LTESpectrumPHY::StartRX () function is called, the SpectrumInterferenceModel is used to computed the SINR, as proposed in . Then, the network device uses the AMC module to map the SINR to a proper CQI and to send it to the eNB using the ideal control channel.
Details about the MAC model:
ENodeBNetDevice and UENetDevice (that are inherited from the LTENetDevice) classes are created to model both eNB and UE devices. The most important component I inted to develop dor both devices are the LTE Spectrum Physical, the AMC Module, the Bearer Manager. Furthermore, for the eNB will be defined also the following elements: the Downlink Scheduler, the Frame Manager, and a list of registered UE (used to store information about registered UEs and CQI feedbacks received from them). A bearer class will be implemented to manage one LTE flow between eNB and UE. For each Bearer, both MACQueue and QoSParametersSet will be also developed.
In order to support the Adaptive Modulation and Coding scheme, the AMCModule will be implemented. In LTE networks, the UE measures periodically the channel quality and sends a feedback, the CQI, to the eNB. In this project, the SINR will be obtained mathematically every time that the LTESpectrumPHY::StartRX () function is called and for all sub channels. The CQI is obtained using the mapping function defined in . The CQI feedbacks will be "sent" to the eNB, using the ideal control channel. The eNB uses these feedbacks to take scheduling decisions and select a proper MCS (Modulation and Coding Scheme), as proposed in .
Details about the ideal control channel Control channel keeps a very important role in LTE networks. In fact, it is responsible of the transmission of several information (i.e., CQI feedback, allocation map, etc...). For this reason, also in a framework oriented to data transmision, it is necesary to find a tecnique for exchange these information. To this aim, an ideal control channel will be developed. Example: CQI feedback. when a UE sends a CQI feedback, it modifies directly the value into a UERecord of the eNB. Example: PDCCH information about downlink map. After scheduling decision, the eNB modifies directly informations about downlink and uplink resources map to the physical object of the UE that will receive/send packets.
 N. Baldo and M. Miozzo, Spectrum-aware Channel and PHY layer modeling for ns3, Proceedings of ICST NSTools 2009, Pisa, Italy.
 3GPP TS 25.814 ( http://www.3gpp.org/ftp/specs/html-INFO/25814.htm )
 Giuseppe Piro, Luigi Alfredo Grieco, Gennaro Boggia, and Pietro Camarda", A Two-level Scheduling Algorithm for QoS Support in the Downlink of LTE Cellular Networks", Proc. of European Wireless, EW2010, Lucca, Italy, Apr., 2010 ( draft version is available on http://telematics.poliba.it/index.php?option=com_jombib&task=showbib&id=330 )
 3GPP R1-081483 (available on http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_52b/Docs/R1-081483.zip)