Ieee 802.11 Enhancements

Transcript

IEEE 802.11 enhancements Standard Year Description Standard Year Description 802.11c 2001 Wireless Bridging 802.11T - Wireless Performance Prediction (WPP) 802.11d 2001 Roaming 802.11u 2011 Interworking to non-802 networks 802.11e 2004 Quality of Service 802.11v 2011 Network management 802.11F 2003 Handover 802.11w 2009 Security for management frames 802.11h 2006 DFS (Dynamic Frequency Selection) and TPC (Transmission Power Control) 802.11y 2008 3.6 GHz for USA 802.11i 2004 Security 802.11z 2010 Direct Link Setup (Ad-hoc) 802.11j 2004 5 GHz for Japan 802.11aa MAC Enhancements for Robust Audio Video Streaming 802.11k 2007 Radio resource measurement 802.11ac MIMO + QAM (5GHz) 802.11m 2006 Maintenance 802.11ad Beamforming + QAM (60GHz) 802.11n 2009 MIMO 802.11ae Prioritization of Management Frames (QoS) 802.11p 2010 Car-to-Car communication 802.11af TV Whitespace (Sub-1GHz) 802.11r 2010 Fast Handover (VoIP) 802.11ah Ultra-low-power version of Wi-Fi with immediate benefits for the so-called "Internet of things“ (Sub-1GHz) 802.11s 2011 Meshed networks 802.11ai Fast Initial Link Setup Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 140 Chair Systems www.tu-cottbus.de/systeme WLAN: IEEE 802.11e • Scope – – • Dates and Facts – – – • Published in 2005 Now part of IEEE 802.11ma Complies to WMM certificate of WiFi alliance MAC Extend – DCF mandatory (RTS/CTS optional) PCF optional (lower jitter than DCF regarding QoS but still no guarantees) Best effort design EDCF/EDCA and HCF/HCCA Prioritization in EDCF Point Coordination Function (PCF) HCF Contention Access (EDCA) Used for Contention Services, basis for PCF and HCF HCF Controlled Access (HCCA) • Key Concept – – – TXOP (Transmission opportunity) EDCA TXOP  contention-based channel access TXOP HCCA TXOP  HCF controlled channel access TXOP • Hybrid Coordinator (HC) – WMM : Wireless Multi Media HCCA: HCF Controlled Channel Access EDCA: Enhanced Distributed Channel Access Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Hybrid Coordination Function (HCF) IEEE 802.11-2007 MAC Layer (Src: 802.11-2007, p. 251) 802.11e MAC – – Required for Parameterized QoS Services Distributed Coordination Function (DCF) Legacy 802.11 MAC – – • Extension of standard MAC layer functionality in order to provide QoS Necessary for delay sensitive applications (e.g. A/V Streaming) Required for Prioritized QoS Services Required for ContentionFree Services for non-QoS STA, optional otherwise Chapter 3 – Page 141 Centralized; higher prioritized access than EDCF Chair Systems www.tu-cottbus.de/systeme IEEE 802.11e – EDCA I • Prioritization through 4 Access Categories (ACs) – – • Each MSDU is mapped to one AC Each AC has its own queue and its own parameter set to contend for TXOP Parameter Set is given by AP (or default if not) and consists of: – – Individual AIFS (Arbitrary IFS): AIFS ≥ DIFS Individual CW (Contention Window) to generate random backoff counter Priority UP AC Description Lowest 1 AC_BK Background 2 AC_BK Background 0 AC_BE Best Effort 3 AC_BE Best Effort 4 AC_VI Video 5 AC_VI Video 6 AC_VO Voice 7 AC_VO Voice Highest Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II (MSDU, UP) Mapping to Access Category Transmit queues for ACs Per-queue EDCA functions with Internal collision resolution Concept of 802.11e MAC layer to provide prioritization: Different queues for each priority (Src: 802.11-2007, p. 287) Chapter 3 – Page 142 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11e – EDCA II • Internal collision: backoff counters of two or more ACs get 0 simultaneously – – • Solution: higher prioritized AC gets TXOP (TXOP = time interval to send data) AC(s) that lost contention react like collision would be external (on wireless medium) External collision: backoff counters of two or more stations get 0 simultaneously – Solution: CW is increased  next backoff counter will be higher 802.11e EDCA: At least a station has to wait for AIFS=DIFS before it is allowed to count down its backoff. (Src: 802.11-2007, p. 258) Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 143 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11e – HCCA I • HCF (Hybrid coordination function) – Only usable in infrastructure QoS network configurations – To be used during both the contention period (CP) and the contention free period (CFP) – Uses a QoS-aware point coordinator („hybrid coordinator“) • by default collocated with the enhanced access point (QAP) • uses the point coordinator's higher priority (PIFS < DIFS) to allocate transmission opportunities (TXOPs) to stations (AIFS ≥ DIFS) – Meets predefined service rate, delay and/or jitter requirements of particular traffic flows – Caused long delays in standardization process due to its complexity Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 144 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11e – HCCA II Flexible multiplexing of CP and CFP in 802.11e MAC. RTS/CTS remains optional. (Src: Mangold, S., Choi, S., May, P., Klein, O. & Hiertz, G. IEEE 802.11e Wireless LAN for Quality of Service. European Wireless (2002)) • In CP there are 2 ways a station (in detail AC of a station) could get TXOP: – – • Medium is idle for (AIFS + Backoff counter) Station receives QoS CF-Poll frame from HC (HC can send QoS CF-Poll frame if medium is idle for PIFS) In CFP start and duration of TXOP is determined by HC (Beacon or CF-End) – Stations cannot get access to medium by itself Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 145 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11e – Conclusions • Legacy 802.11 MAC vs. 802.11e MAC – Multiplexing of CPs and CFPs is flexible in 802.11e whereas it was fixed in legacy standard – In 802.11e HC sends periodically beacon frames like in 802.11 legacy standard  stations still have to register at HC in CP in order to get part of polling list  that is one reason why duration of CFP is bounded in 802.11e, too – In 802.11e prioritized (EDCA) and parameterized (HCCA) QoS is provided • Remaining Problem: – Additional effort is necessary if several BSS/QBSS in overlapping physical space work concurrently – The protocol is still based on “listen before talk” thus priority services can only be started if the medium is free. This leads to varying delay and delay yitter Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 146 Chair Systems www.tu-cottbus.de/systeme WLAN: IEEE 802.11s • Scope – Extension of standard MAC layer to support wireless LAN mesh topologies – Inside mesh: all mesh stations establish wireless links with neighbor stations in order to mutually exchange messages – multi-hop capability: message transfer between stations that are not connected directly • Required for Parameterized QoS Services Required for Mesh Coordination Contention-Free Function (MCF) Services for nonQoS STA, Optional Hybrid Coordination otherwise Function (HCF) Used for Contention Services, basis for PCF, HCF, MCF Extend Dates and Facts Distributed Coordination Function (DCF) IEEE 802.11-2012 MAC Layer (Src: 802.11-2012, p. 818) 802.11s MAC – EDCA (Extended Distributed Channel Access) and MCCA (Mesh Coordinated Channel Access – Mesh stations are QoS stations that support mesh services – Mesh stations implement subset of QoS functionality Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Required for Prioritized QoS Services MCF HCF/MCF Point HCF Coordination Controlled Controlled Contention Access Access Function Access MAC (MCCA) (EDCA) (PCF) (HCCA) – Published in 2011 – Now part of IEEE 802.11mb • Required for Controlled Mesh Services • Mesh functionalities Chapter 3 – Page 147 – – – – – – Formation Path selection Forwarding Security Power Management Intra-mesh congestion control Chair Systems www.tu-cottbus.de/systeme 802.11s: Unwire the WLAN with Mesh Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 148 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – Overview I • • A station starts transmission of beacons and performs a synchronization procedure in order to start a new MBSS (Mesh Basic Service Set) or to become member of a MBSS No central entity in a MBSS: In a legacy BSS a station gets associated with an AP  in a MBSS a mesh station peers with other mesh stations MBSS forms a single set of independent/autonomous mesh stations • • • • • • For a mesh station that has not become member of a MBSS the “mesh discovery service” is available Inside the mesh all stations have wireless links with their neighbors Multi-hop capability: messages can be transferred between stations that are not in direct communication From a data delivery point of view: all stations in a MBSS are (logically) directly connected at MAC layer Stations in a MBSS can act as sources, sinks or propagators of traffic A MBSS might have interfaces to external networks (mesh gates and portals) Stations use Mesh Coordination Function (MCF) to access the channel Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 149 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – Overview II • Mesh Point (MP): establishes peer links with MP neighbors, full participant in WLAN Mesh services  Light Weight MP participates only in l-hop communication with immediate neighbors (routing = NULL) • Mesh AP (MAP): functionality of a MP, collocated with AP which provides BSS services to support communication with STAs • Mesh Portal (MPP): point at which MSDUs exit and enter another IEEE802.x network • Station (STA): outside of the WLAN Mesh, connected via Mesh AP Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 150 MP Chair Systems www.tu-cottbus.de/systeme Complex Meshed Network Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 151 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – Services I • • Mesh discovery Mesh peering management – Direct communication between 2 mesh stations only allowed if they are peer mesh stations  after mesh discovery: establish a mesh peering to each other • Mesh security – Mesh link security protocols to authenticate a pair of mesh stations (session keys) – Mesh authentication protocols establish a shared, common pairwise master key • • Mesh beaconing and synchronization Mesh coordination function (MCF) – Channel access: consists of EDCA (contention-based) and MCCA (reservation based) – MCCA: to optimize efficiency of frame exchanges in MBSS • Mesh power management – Mesh station is able to manage activity level of its links via mesh peering – Active mode, light sleep mode or deep sleep mode • Interworking with Distribution System (DS) – MBSS contains ≥ 0 mesh gate(s) that connects to DS Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 152 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – Services II • Mesh path selection and forwarding – – – – Hybrid wireless mesh protocol (HWMP): default path selection protocol Proactive and reactive path selection uses link metrics; default: airtime link metric If mesh path from source to destination mesh station was found: mesh stations propagate the data by forwarding function – Result: data is transmitted among all mesh stations in a MBSS (even if stations are not neighbors of each other) • Intra-mesh congestion control – Used to provide flow control over multi-hop communication – Aim: reduce wasteful wireless medium utilization caused by buffer overflow at mesh stations – 3 main mechanisms  Local congestion monitoring and detection  Congestion control signaling  Local rate control Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 153 Chair Systems www.tu-cottbus.de/systeme Airtime Link Metric Function • A default link metric to be used by a path selection protocol to select the best paths. – Other metrics can also be used. • Its cost function is based on airtime cost (Ca), which reflects the amount of channel resources consumed by transmitting the frame over a particular link.  Bt  1 ca  O   r  1 e f  Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Parameter Description O Channel access overhead including frame headers, training sequences, access protocol frames, etc (depending on PHY) Bt Test frame length in bits (Constant) r Transmission data rate in Mb/s for the test frame size Bt ef Test frame error/loss rate for Bt Chapter 3 – Page 154 Chair Systems www.tu-cottbus.de/systeme Example  Unicast Cost Function based on Airtime Link Metrics 54Mb/s, 8% PER 48Mb/s, 10% PER 54Mb/s, 2% PER 54Mb/s, 2% PER 12Mb/s, 10% PER 48Mb/s, 10% PER This path having the minimum airtime cost is the Best! Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 155 Chair Systems www.tu-cottbus.de/systeme Hybrid Wireless Mesh Protocol (HWMP) • A default path selection protocol for interoperability. • To combine the flexibility of on-demand route discovery with extensions to enable efficient proactive routing to mesh portals. – On-demand mode • Used in intra-mesh routing for the route optimization • When a root portal is not configured or it can provide a better path even if root is configured. – Proactive, Tree based mode • If a root portal is present, a distance vector routing tree is built. • Tree based routing avoids unnecessary discovery flooding during discovery and recovery Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 156 Chair Systems www.tu-cottbus.de/systeme HWMP: On-demand Path Selection Mode 1. Source broadcasts PREQ (path request) with the destination and metric initialized. 2. Upon receiving PREQ, MPs update the path to source if sequence number is greater and offers a better metric 3. If a new path is created or the existing one is modified, PREQ is forwarded further. 4. PREQ provides “Target only” (TO) and “Reply and Forward” (RF) flags. • If TO=1: Only destination sends PREP (path reply) after selecting best path. • If TO=0 and RF =0: Intermediate node with path sends a unicast PREP to the source MP and does not forward PREQ • If TO=0 and RF =1: The first intermediate node with the path to the destination sends a PREP and forwards PREQ setting TO =1 to avoid other intermediate nodes to send back PREP. 5. When source receives the PREP, it creates a path to the destination. Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 157 Chair Systems www.tu-cottbus.de/systeme HWMP – Proactive tree building mode • • Proactive PREQ mechanism – Root MP periodically broadcast PREQ – To create paths between the root mesh and all mesh nodes in the network proactively (2-way handshaking) Proactive RANN mechanism – Root MP periodically broadcast RANN – Distribute path information for reaching the root mesh but the actual paths to the root mesh can be built on-demand (3-way handshaking) Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 158 Chair Systems www.tu-cottbus.de/systeme Example – Proactive PREQ mechanism PREP R PREQ 1) The root MP periodically propagates a PREQ into the network - Destination Address set to all ones - The TO flag set to 1 and the RF flag set to 1 2) Upon reception of a PREQ, each MP has to create or refresh a path to the root MP 3) The recipient MP’s action - If “Proactive PREP” bit set to 0, MP may send a proactive PREP if required. - If “Proactive PREP” bit set to 1, MP shall send a proactive PREP. 4) Tree path construction is completed Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 159 Chair Systems www.tu-cottbus.de/systeme Example – Proactive RANN mechanism PREP 1) The root MP periodically propagates a RANN into the network. R RANN PREQ 2) Upon reception of a RANN, each MP has to create or refresh a path to the root through sending a unicast PREQ to the root MP. 3) The root MP sends a PREP in response to each PREQ. 4) Tree path construction is completed Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 160 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – MCF • Concept of transmission opportunity (TXOP) is used – Defined through starting time + maximum length • EDCA TXOPs and MCF controlled channel access (MCCA) TXOPs – EDCA: contention-based  same EDCA as for HCF – MCCA: mesh stations are able to access wireless medium at pre determined times with lower contention probability than otherwise possible • MCCA TXOP – Management frames to make reservations  initiating mesh station sends a request (owner of reservation) and other mesh stations receive request (responders) – Owner and responder advertise the reservation to neighbor mesh stations – Neighbors shall not initiate a transmission during these reserved intervals → Owner obtains TXOP by winning an instance of EDCA because there is no competition as a result of reservation – Synchronization with neighbor mesh stations required – Mesh stations shall track reservations of neighbors – Tracking means: recording reservations  recording advertisement set sequence number, advertisement elements bitmap and advertisement element indexes in a local database Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 161 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11s – Conclusions • • Extensions specified to create a wireless distribution system with automatic topology-learning and wireless path configuration Dynamic, radio-aware path selection inside MBSS • Possible application: unwire the WLAN with mesh networks – Wireless paradox: WLAN access points are typically wired – Mesh networks provide possibility to establish a robust and reliable broadband service access at reasonable cost – Mesh networks are dynamically self-organized + self-configured  nodes in a mesh network automatically establish + maintain connectivity – Backbone nodes of mesh network in general are not mobile (in contrast to MANETs) – Advantages for end users: • Low up-front costs • Easy network maintenance • Robustness • Reliable service coverage Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 162 Chair Systems www.tu-cottbus.de/systeme WLAN: IEEE 802.11k • • Scope Benefit/Value – Standardized measurements across vendors – Collected data is made available to management and upper protocol layers – Simplify configuration – Better diagnostic of errors – Enable new services – Can help to optimize network performance – WLAN Radio Resource Measurements – Enable stations to observe and gather information on wireless environment and radio link performance • Dates and Facts – Published in 2008 – Now part of IEEE 802.11-2012 • Usage – Enable stations to do measurements locally – Enable stations to request measurements from other stations – Enable stations to be requested by other stations to make measurements • • Radio Resource Measurements Service can extend: Applications – Voice and Video over IP, location based applications Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 174 – Capability – Reliability – Maintainability Chair Systems www.tu-cottbus.de/systeme IEEE 802.11k – Mechanisms I • Most mechanisms use request/report scheme  A station can request measurements from other stations and results are reported back in standardized frames • Statistical measurements – Characterization of radio environment in long-term statistical sense • Identity measurements – Identify stations for different purposes Request/Report Request-only Report-only Beacon Measurement Pause Measurement Pilot Frame Channel Load Noise Histogram STA Statistics Location Configuration Information (LCI) Neighbor Report Link Measurement Transmit Stream/Category Measurement Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 175 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11k – Mechanisms II • Beacon: – Request from another station a list of APs that requesting station can receive on specified channel(s) – Active/passive mode like active/passive scanning – Active: probe request and monitoring afterwards – Passive: just monitoring of channel (listen and collect) – Beacon table mode: no additional measurements  only report current content of any stored beacon information • Measurement Pilot – Compact action frame  subset of information of a beacon frame (smaller packet) – Transmitted periodically by AP, more often than beacon – Purpose: assist station with scanning • Frame – Returns picture of all channel traffic in a per transmitter station fashion: – TX address, number of frames received from TX, average power level for these frames, BSSID of TX • Channel Load – Returns channel utilization measurement of measuring station Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 176 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11k – Mechanisms III • Noise Histogram – Returns power histogram of all non-802.11 energy • STA statistics – Returns different counters of measuring station and BSS average delays: – frame counts (RX, TX, RTS, CTS), failed counts, retry counts, multiple retry counts, duplicate frame counts, ACK failure counts, … – AP average access delay, average access delay for each AP, … • Location – Returns requested location (latitude, longitude, altitude): Where am I? or Where are you? – Various reporting resolutions possible • Measurement Pause – Permits control of measurement period when measurement request frames are to be repeated • Neighbor request – Request is sent to AP, AP returns report – Report: known neighbor APs that are candidates for a service set transition  potential roaming candidates Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 177 Chair Systems www.tu-cottbus.de/systeme IEEE 802.11k – Mechanisms IV • Link Measurements – Provide RF characteristics of station-station link  instantaneous quality of the link • TX stream/category measurement – Enables a QoS station to request of a peer QoS station the condition of an ongoing traffic stream link between them (QoS station-QoS station stream link) Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 178 Chair Systems www.tu-cottbus.de/systeme WirelessHART (DIN EN 62591) • Scope – – • – – Published in 2007 by HART Communications Foundation (HCF) First open industrial wireless communication standard Operation in 2.4 GHz ISM band WirelessHART vs. HART – – – • Command-oriented data types + applications Transport Layer Reliable stream, support large data set Network Layer Self-healing, Low-Power, Mesh Network Logical Link Control MAC Sublayer Secure + Reliable, TDMA / CSMA Physical Layer 2.4 GHz, IEEE 802.15.4 based radios Dates and Facts – • Extension of Highway Addressable Remote Transducer (HART) protocol Benefits in comparison to HART: simplicity, robustness, lower installation- + maintenance costs, flexibility Application Layer Specific physical, data link + network layer Implements IEEE 802.15.4 PHY layer Same transport + application layer of HART protocol WirelessHART protocol stack (Src: The Art of Wireless Sensor Networks, Vol. 1, Chapter 23) • Key Concepts – Features – – Secure, highly reliable, TDMA-based, selforganized + self-healing wireless mesh technology FHSS, blacklisting, DSSS Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II – Chapter 3 – Page 179 – – time-synchronized data link layer to meet timing requirements of industrial process automation TDMA for collision-free deterministic coordinated communication Central network manager to maintain knowledge of topology, manage routing + handling assignments of routing tables 2 types of routing: graph + source routing Chair Systems www.tu-cottbus.de/systeme WirelessHART: IEEE802.15.4 + Extension • • • • Das Spreading Verfahren ist „Slow FHSS“ Im Basisband wird optional zusätzlich Barker Spreading eingesetzt. Das verringert die Datenrate um den Faktor 11, erhöht den Systemgewinn aber um >10dB Es stehen 15 Frequenzbänder (je 2 MHz; 5MHz Kanalabstand) und 15 Zeitslots für die Kommunikation zur Verfügung Alle 10ms wird innerhalb eines Superframes ein neuer Funkkanal gewählt um Fading Effekte zu vermeiden Ein Zeit- Frequenzslot ist die kleinste Ressource Jedem Paar von Kommunikationsknoten kann eine Menge solcher Ressourceblöcke für die Kommunikation zugeordnet werden Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 180 11 12 13 14 15 16 Channel • • 17 18 19 20 21 22 23 24 25 Time Chair Systems www.tu-cottbus.de/systeme Systembeispiel 2: PSSS • • • • Der Systemansatz basiert auf einem Closed-Loop Verfahren mit zentral gesteuertem Medienzugriff Vorschlag für ein neuartiges PSSS basiertes Funksystem mit hoher Störfestigkeit und sehr kurzer Latenzzeit Ein zyklischer m-Code erzeugt parallele, orthogonale Datenströme Datenraten bis 20 Mb/s bei Latenzzeiten von 10 ms, PER von 10-9 Codes Ressource Block Client 1 2 3 …. Präambel 1 PSSS255-Symbol Chips 254 255 254 255 254 255 … Upstream by FDD, TDD or CDD ….. ….. ….. Station 3 3 3 Client 2 2 2 2 Master 1 1 1 Concurrent downstream 253 254 255 Client n Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II Chapter 3 – Page 181 Chair Systems www.tu-cottbus.de/systeme Systembeispiel 3: Cognitive IR-UWB (802.15.4) • • • • • UWB basiert auf BreitbandÜbertragung im 3,4-10,5 GHz Band Die spektrale Sendeleistung ist auf -41dBm/MHz begrenzt UWB kann als Underlay-System parallel zu anderen Funksystemen betrieben werden Durch kognitive Kanalwahl können die Funkknoten auf störungsfreie Kanäle ausweichen Scanner beobachten die Funkumgebung und stellen die Informationen über die Kanalbelegung durch Fremdsysteme zur Verfügung Wednesday, 14 January 2015 Winter Term 2014 – Mobile Communications II UWB Knoten UWB Knoten Scanner Scanner UWB Knoten UWB Knoten Scanner Kognitives Lernsystem MIB Kognitives Signalisierungssystem Chapter 3 – Page 182 Chair Systems www.tu-cottbus.de/systeme