Autonomous Infrastructure Wireless Networks: A Perspective on 4G

Transcription

1 Autonomous Infrastructure Wireless Networks: A Perspective on 4G Elvino S. Sousa Jeffrey Skoll Chair in Computer Networks and Innovation Wireless Lab University of Toronto Canada 1

2 Wireless System Evolution Cellular Systems 1G, 2G, 3G, Extension of telephone network to mobile IEEE (WiFi) a/b/g/e/n versions Extension of LAN s to wireless Infrastructure mode Ad-hoc mode Extension of Internet access to wireless IEEE (WiMax) Extension of ATM to wireless Wireless video transmission 2

3 Evolution 1G => 3G Evolution from 1G to 3G stressed higher bit rates and greater network capacity for a given amount of spectrum. Centrally planned network More or less equal capacity per cell. More or less regular cellular structure. Regular cells, micro cells, pico cells Cost of base station/access point deployment is a key issue. 3

4 4G Themes No clear set of goals for 4G Various attempts to combine different technologies: 3G, WiFi, WiMax => convergence Some indications that the main issue is not some notion of network capacity but different networking/deployment paradigms Re-evaluate all assumptions about cellular systems: FDD/TDD, non-symmetric allocation of spectrum, cell sizes, base station/terminal/relays, very high data rates, etc.. 4

5 Emergence of WLAN s IEEE networks becoming quite popular Free air time Restricted to some hotspots lack of wide area coverage Security issues Not designed to be an interface for access to infrastructure but rather for peer-to-peer, but being used for infrastructure Efficiency of air interface? Congestion? Seamless wide-area operation? 5

6 Integration of Cellular and WLAN s Integration of cellular and WLAN s into seamless network is possible Seamless inter-operability may be complex Not clear as to the cost 6

7 Required Network A network architecture with the characteristics of WLAN s in the sense that it allows inexpensive adhoc deployment of infrastructure. A network architecture with the characteristics of 3G: channelized, ubiquitous, interference control, spectral efficiency Seamless inter-operation with wide-area backbone network (cellular-like) Single unified air-interface and access point interconnection network based on IP Ease of deployment and management 7

8 Proposed System Consumer driven access point (AP) or micro-base station 100 s of dollars instead of 10,000 s Compete with WiLAN AP s Network infrastructure grows organically => driven by users, or operating company, or a mixture Centralized network interference management utility Based on modified 3G Technology and evolution CDMA2000+, or WCDMA+, GSM+ Needs new physical layer functions for environment sensing, auto-configuration, and base station sleeping modes Advantages: Hot spot coverage + wide area coverage + unified physical layer 8

9 Advantages over WLAN s Synergy with wide-area network Circuit switching => possibly better security 3G technology was actually designed for infrastructure Power control, interference management 3G is at home in this cell-based environment, WLAN is not! 9

10 Generalized Wireless Network Architectures Traditional Cellular Systems: Base stations: fixed, arranged in a regular pattern throughout service area Terminals: mobile 4G Networks Shared equipment: Base station, access point, repeater/relay, fixed or mobile Dedicated equipment: terminal, fixed or mobile. 10

11 Proposed System Architecture 11

12 Autonomous Network Architecture Broadband IP core network with common interface Network Access Point (NAP) LAN, DSL, CATV, PLC, WiFi, WiMax, other broadband wireless Devices with two interfaces: 1) NAP, 2) autonomous network interface Cell Access Point (CAP), different characteristics in terms of size and functionality SCAP small power, serves a small number of terminals, sleep modes, etc LCAP large power, serves large number of terminals, may or may not have sensing capability Network divided into a number of geographical regions: network control domains Each domain is managed by a server: Spectrum Power & Antenna configuration Manager (SPAM) SPAM connects to and configures the CAP s over the IP network SPAM s connect to a Global Network Controller (GNC) for global configuration functions Sleep mode specification for SCAP Wake-up function for terminals 12

13 Possible Air-Interfaces that can be Used in the Initial System CDMA2000 1X system CDMA2000 1X based system with the incorporation of a sleep mode, i.e. small modifications to CDMA200 1X WCDMA based systems (with and without sleep mode) Other Wideband based CDMA system 1X EV/DO system with and without sleep mode Evolving 3G air interface based on the use of MIMO. Evolving 3G/OFDM air interface with sleep mode. 3G/LTE with enhancements All of these interfaces assume the capability for the transmission of a pilot signal with a code that identifies the access point to the system Manager. This function is required for the automatic configuration of the access points. GSM evolved system WiFi evolved system WiMax evolved system 13

14 Cellular Access Point Characteristics The access point can be configured with a given pilot transmission power The allowable range of transmitter powers will determine the cost of the access point and ultimately its deployment strategy Very low power access points will be inexpensive and can be bought and installed by the users - autonomous installation High power access points require coordinated installation by an RF specialist, subject to health regulatory requirements, and general RF interference considerations 14

15 Access Point Functionality State: the AP is on or off. It is always on for large base stations, and for small stations it is in sleep mode if there is no traffic. The access point reports its antenna configuration (e.g. beam forming) to the manager. This applies to the case where the access point utilizes an antenna array (which may consist of as few as two elements). Sleeping CDMA/GSM micro base-stations: Hey I am here! keep it down! can I help you? 15

16 Access Point Functionality cont. The access point reports its transmitter power to the manager The access point may (optionally) report its GPS (Global Positioning System) coordinates to the manager, if it has GPS capability The access point measures the signal strength on all the pilots that it hears from neighbouring AP s and transmits them back to the manager A vector of coordinates are transmitted with individual entries being a pair (base station ID, pilot power received) The access point may have the capability to transmit a wake-up message to neighbouring access points in order to get them to transmit a signal so that their pilots can be received and the manager can establish an interference matrix between access points. 16

17 Access Point Installation Two main approaches By a network operator using a similar methodology to that currently used to install base stations. This involves coverage considerations, leasing arrangements, RF radiation considerations with respect biomedical issues, etc. By a user in an autonomous manner. This may be as a result of lack of capacity in a certain area or the cost to use another access point. This is driven by the user in response to some specific needs and the installation process is similar to that of an access point for a current WiFi network. 17

18 SPAM (Controller) Optimize pilot power and antenna configuration for each CAP, cell site parameters such as pilot offset, or code, parameters in synch channel Example Algorithm (LCAP) Periodically dedicate one slot in a large time where only pilot and synchronization signals are transmitted (all traffic signals off) In this slot the different CAP s transmit pilots and synch signals. This slot should have a small duty cycle so as to decrease overhead. Considering a small fraction of the above slot, the different CAP s go into listening mode staggered so as to make power vector measurements. Slot time should be large enough to ensure sufficient processing gain for measurement 18

19 SPAM Controller - cont Example algorithm SCAP All CAPs are in sleep mode Terminal transmits a wake-up signal Signal received by a number of CAPs all send power measurement to Controller Controller then determines the maximum (or close to max) and commands that CAP to respond to terminal Depending on traffic loads the Controller may not assign the terminal to the CAP receiving the max 19

20 Wireless Network Evolution Currently wireless system evolution in 3G, WiMAx, WiFi, convergence approaches Key for 3G: ad-hoc deployment with unified interference management Key for WiFi: better approaches for interference management, cellularization Autonomous infrastructure: Facilitate the deployment of large scale networks with unified air interface => coverage and interference management Hot spot high capacity cells Organic growth 20

21 Evolution of Cellular Systems 1G - Analog, 800 MHz band, FM modulation, regular cell deployment 2G - digital, primarily voice, single rate service, low rate data, compatibility with analog (NA), roaming, regular cell deployment 3G - variable data rate service, higher data rates (up to 2 Mbps), somewhat regular cell deployment. 4G - autonomous cellular, sleeper base stations, the network grows organically, highly irregular cell deployment, smart network architecture, all the network smarts are contained in the network control server - the Manager. The plug-and-play base station! 21