femtocellintroduction

femtocellintroduction内容摘要：

ronization, and backhaul  Voice femtocells  Interference management in femtocells, allowing access to femtocells, handoffs, mobility, and providing Emergency 911 services  Network infrastructure  Securely bridging the femtocell with the operator work over IP Technical Challenges － Broadband Femtocells (1/4) 18  Two main problems operators face: mitigate RF interference, efficiently allocating spectrum  The RF interference will arise from:  Macrocelltofemtocell interference (nearfar effect)  Femtocelltofemtocell interference  Femtocelltomacrocell interference (nearfar effect) Technical Challenges － Broadband Femtocells (2/4) 19  Challenge 1: How Will a Femtocell Adapt to Its Surrounding Environment and Allocate Spectrum in the Presence of Intra and CrossTier Interference?  Since femtocells will be placed by end consumers, the ad hoc locations of femtocells will render centralized frequency planning difficult  Decentralized spectrum allocation between macrocell and femtocell users is an open research problem  Should macrocell and femtocell users be orthogonal through bandwidth splitting? As 3GPP LTE and WiMax  Alternatively, with shared bandwidth  Which of these two schemes is “better” in various configurations? Technical Challenges － Broadband Femtocells (3/4) 20  Challenge 2: How Will Femtocells ProvideTiming and Synchronization?  Synchronization  Align received signals to minimize multiaccess interference  Macrocell users can handoff to a femtocell or vice versa  Timing  Immune to packet jitter  Network solutions such as the IEEE1588Precision Timing Protocol over IP and selfadaptive timing recovery protocols(. ) are promising  Equip femtocell with GPS(synchronized with the macrocell)  Highprecision ovencontrolled crystal oscillators may be used Technical Challenges － Broadband Femtocells (4/4) 21  Challenge 3: How Will Backhaul Provide Acceptable QoS?  IP backhaul needs QoS for delaysensitive traffic and sufficient capacity  Lack of neutrality poses a serious concern  Another issue: when users employed WiFi, femtocells experienced difficulty transferring data and even lowbandwidth services like voice[5] [5] Presentations by ABI Research, Picochip, Airvana, , Gartner, Telefonica Espana, 2nd Int’l. Conf. Home Access Points and Femtocells。 Technical Challenges － Voice Femtocells (1/6) 22  Two choices:  Allocate different frequency bands to macrocell and femtocell users  Eliminate crosstier interference  Serve both macrocell and femtocell users in the same region of bandwidth (preferable)  Maximize area spectral efficiency Technical Challenges － Voice Femtocells (2/6) 23  Challenge 4: How Will Femtocells Handle CrossTier Interference?  CDMA works (without femtocells) employ fast power control to pensate for path loss, sh。