ECE 414 WIRELESS COMMUNICATIONS. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

Transcription

1 ECE 414 WIRELESS COMMUNICATIONS O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

2 Chapter 1 Overview of Wireless Communications O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

3 Outline of Chapter 1 Ø Brief History of Wireless Communications Ø Basic Terminology Ø Examples of Wireless Communication Systems Paging Systems Cellular Radio Communications Wireless Metropolitan Area Networks (WMANs) Wireless Local Area Networks (WLANs) Wireless Personal Area Networks (WPANs) Slides based on textbook and previous offering by Profs. Zhuang and Uysal. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

4 Brief History of Wireless Communications Early Days Ø Guglielmo Marconi demonstrated wireless telegraph concept to English telegraph office Ø The Birth of Radio - Marconi awarded patent for wireless telegraph Ø 1898 The (first commercial) wireless telegraphic connection was established between England and France Ø First Transoceanic Communication- Marconi successfully transmits radio signal across Atlantic Ocean from Cornwall to Newfoundland Ø First voice-over-radio transmission Ø 1920/30s - Mobile communication adopted for police vehicles in USA Ø Armstrong introduced Frequency Modulation (FM). FM has been the primary modulation technique for mobile communication systems until late 80s. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

5 Brief History of Wireless Communications Birth of Mobile Telephony Ø First interconnection of mobile users to public switched telephone network (PSTN) was introduced in 25 major American cities. A single, high-powered transmitter is used in order to cover distances over 50 km. The entire spectrum is allocated on an FDMA basis, where each user is assigned a dedicated frequency. If the number of channels (i.e. available frequency carriers) is given by C, only C users per geographic area can be served. Half-duplex mode operation, i.e. only one person on the phone call could talk at a time. A certain channel occupies 120kHz bandwidth (although the actual telephone-grade speech occupies only 3kHz) due to inefficient RF filter designs O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

6 Brief History of Wireless Communications Birth of Mobile Telephony Ø 1960s - Improved Mobile Telephone Service (IMTS) was introduced. IMTS supports full-duplex, i.e. two parts can talk simultaneously. IMTS supports auto-dial, i.e. no operator s assistance. IMTS supports auto-trunking, i.e. no dedicated frequency. Therefore, it is possible to sell mobile equipment to more than C users by assigning channels on a demand basis satisfying a certain blockage probability. Ø 1970s - IMTS quickly became saturated in major markets. For example, in 1976, Bell Mobile Phone service for the New York City area had only 12 channels and could serve only 543 customers; service was poor due to call blocking due to the few available channels. Ø 1970s - Cellular concept was introduced: This involves breaking a coverage zone into small cells (regions), each of which reuse portions of the spectrum to improve efficiency of spectrum usage (more details to follow later in this chapter). Ø NTT (Japan) introduced first commercial cellular phone system. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

7 Basic Terminology- I Ø Downlink (Forward) channel: Base station à Mobile station Ø Uplink (Reverse) channel: Mobile station à Base station Ø Simplex (SX) transmission: One way communication from one point to another, e.g. radio/tv broadcasting stations, paging systems. Ø Half-duplex (HDX) transmission: Information can flow in both directions, but the flow is only one-way at any given time, e.g. dispatch radio systems (push-to-talk), walkie-talkie. Ø Full-duplex (FDX) transmission: Simultaneous communication in both directions, e.g. phone. There are two ways to implement FDX transmission: Frequency Division Duplex (FDD) uses two simultaneous, but separate channels. Time Division Duplex (TDD) uses adjacent time slots on a single radio channel. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

8 Basic Terminology- II Ø Frequency Division Duplex (FDD) BS à MS MS à BS f F f R frequency At the base station, separate transmit and receive antennas are used to accommodate two separate channels. At the mobile station, a single antenna (through the use of a duplexer ) is used for both transmission to and reception from the base station. To provide sufficient isolation, f R f F >1.05 O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

9 Ø Time Division Duplex (TDD) Basic Terminology- III F.C. R.C. F.C. R.C. F.C. R.C. time TDD is only possible with digital transmission formats. If the data transmission rate in the channel is much higher than the end-user s data rate, it is possible to store information bursts and provide the appearance of full duplex operation to a user, although there are not two simultaneous radio transmissions at any instant. Guard times must be used to account for variable propagation delays. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

10 Ø Multiple Access Methods Basic Terminology- IV In the reverse link (uplink), multiple MSs transmit to the BS, i.e. many-to-one transmission. This mode of transmission is referred to as multiple access. If two or more user signals arrive at the BS at the same time, there will be interference unless the signals are orthogonal. The question is how to maintain orthogonality among the transmitted signals from different users: FDMA, TDMA and CDMA Frequency Division Multiple Access (FDMA): Each user is allocated a portion of the system bandwidth to be used at all times. Time Division Multiple Access (TDMA): Each user is allowed to use the entire system bandwidth for a portion of the time. Code Division Multiple Access (CDMA): Each user is allowed to use the entire system bandwidth all of the time. Each user s signal is distinguished from others through the use of unique signature codes. More details to come in Chapter 6 O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

11 Examples of Wireless Communication Systems Mobile Station Base Station In the following, we will have a deeper look at some popular examples of wireless communications. These are: Ø Paging Systems Ø Cellular Radio Communications Ø Wireless Metropolitan Area Networks (WMANs), Wireless Local Area Network (WLANs) and Wireless Personal Area Networks (WPANs) O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

12 Paging Systems Ø Paging systems are communication systems that send brief messages (numeric, alphanumeric or voice) to a subscriber. Ø System does not need to know the location of the pager. Ø Same message is simultaneously transmitted from each base station, i.e. simulcasting. Each user listens to all transmissions, however only decodes its intended message associated with its unique subscription number. Ø Paging systems are designed to provide very reliable coverage, even inside buildings. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

13 Paging Systems (cont d) Ø Simulcasting can cause multiple versions of the same message to be received at a pager with propagation delays that differ by as much as 80µsec. This result in so-called intersymbol interference (ISI). Ø Rule of thumb: To avoid the need for equalization (more details in Chapter 4), it is necessary to make the pulse duration greater than ~4 times the delay spread. T = 4 80 = 320µ sec s R s 1 = T s 1 = = Hz Ø Hence, simple binary modulation formats are limited to data rates of a few kbps. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

14 Basics of Cellular Radio Communications Ø A cell is a geographical area served by a single base station (femto/pico, micro, macro). Ø Each cell is allocated a group of k channels. Ø N cells form a cluster where all C=kN channels are used. Ø M clusters (each of which includes N cells) cover the entire geographic area, à Each channel is re-used M times. à Each channel is re-used once every N cells. Ø Channels can be re-used when there is sufficient distance between the transmitters to prevent interference à Requires careful planning Ø Cellular concept allows efficient use of scarce frequency spectrum (basically it increases the system capacity by a factor of M). O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

15 Basics of Cellular Radio Communications (cont d) Example: Coverage area for New York City Before Cellular Mobile Telephony After Cellular Mobile Telephony O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

16 Basics of Cellular Radio Communications (cont d) Ø A cellular system consists of mobile stations (MS), base stations (BS) and a mobile switching center (MSC). MSC is connected to wireline network. Public switched telephone network (PSTN), Internet Ø The only wireless communication link in the above configuration is the communication between the MS and BS, but it is also the weakest link of the whole system. Ø The communication system engineer should be able to design a reliable link over the wireless channel, which introduces its own challenges compared to wireline communications. That is what you will learn in this course! O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

17 Basics of Cellular Radio Communications (cont d) Ø A number of channels are assigned as control channels for communication between MS and BS in order to carry non-user data. Ø When a MS is turned on (not yet engaged in a call), it first scans control channels to determine the BS with the strongest signal and monitors that control channel until it drops below a useable level. Ø When a phone call (from wireline phone) is placed to a MS, the MSC sends the request to all BS s. The subscriber identification number is broadcast as a paging message over all of the control channels throughout the cellular system. Ø The MS receives the paging message sent by the BS it monitors and responds by identifying itself over the control channel. Ø The BS relays the acknowledgment sent by the MS and informs the MSC of the handshake. The BS assigns an unused voice channel within the cell for that particular MS and instructs the MS change its frequency to assigned voice channel. Ø Once a call is in progress, the BS adjusts the transmitted power of the mobile (if required) in order to maintain the call quality. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

18 Basics of Cellular Radio Communications (cont d) Ø If the MS moves from one cell to another, a handoff (handover) process (i.e. switching to another BS) enables the call to proceed uninterrupted. Ø When a MS originates a call, a call initiation request is sent on the control channel to the BS. The BS receives the request and sends it to the MSC. Ø The MSC validates the request and makes the connection to the called party through the PSTN. At the same time, it instructs the BS to ask MS to move to an unused voice channel, allowing the conversation to begin. Ø Roaming allows subscribers to operate in service areas other than the one from which service is subscribed. Each MSC keeps track of the users through home location register (HLR) and visitor location register (VLR). If a roaming subscriber is identified, its information is sent to its home MSC which updates the location of its subscriber. Ø If a call is made to a roaming subscriber from any phone in the world, the phone call is routed directly to home MSC. The home MSC checks the HLR to determine the location of subscriber and routes the call to the visited network. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

19 Figure: Timing diagram illustrating how a call to a mobile user initiated by a landline subscriber is established. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

20 Figure: Timing diagram illustrating how a call from a mobile user is established. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

21 Trends in Cellular Radio Communications Ø 1980 s - First Generation (1G): Analog modulation (FM), FDD/FDMA For voice communication From the actual advertisement Briefcase model: You can carry it wherever you go! Ø 1990 and early 2000 s - Second Generation (2G): Digital modulation, FDD/ TDMA or CDMA For voice and low-rate data communication Handheld phones Ø Early 2000 s - 2.5G : Improved data rates over those of 2G. Based on still 2G infrastructure. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

22 Trends in Cellular Radio Communications (cont d) Ø 2000 s - Third Generation (3G): For voice and high-rate data communication supporting internet and various multimedia services such as video telephony, video streaming, on-line gaming etc. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

23 Trends in Cellular Radio Communications (cont d) Ø 2010 s - Fourth Generation (4G): Still higher data rate (with smart phone apps, social networking and HD video streaming in mind.) As well as smoother integration of different networks across the globe. Photo: Apple/Samsung O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

24 Second Generation (2G) Cellular Systems O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

25 2.5G Cellular Systems Ø 2G systems were originally designed for voice communication and low-rate data communication. They use circuit-switched data modems that limit users to data rate of a single voice channel (~10 kbps). Examples for 2G data comm. applications: SMS of GSM, i-mode of PDC in Japan. Ø In an effort to upgrade 2G standards to make it compatible for the increased data rates to support Internet applications (e.g. WAP) and multimedia services, 2.5G standards were introduced. Ø 2.5G allows existing 2G equipment to be used with some hardware/software add-ons at the base station and software upgrades on the mobile station. TDMA-based upgrades: HCSD: High Speed Circuit Switched Data GPRS: General Packet Radio Service EDGE: Enhanced Data Rates for GSM Evolution CDMA-based upgrades: IS-95b O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

26 Third Generation (3G) Cellular Systems Ø 3G standards were developed to support demanding requirements of Internet/ multimedia services. Target minimal data rate is 2Mbits/sec for fixed (indoor) and 144Kbits/sec for mobile (outdoor) environments. Ø International Telecommunication Union (ITU) initiated International Mobile Telephone (IMT-2000) plan with a vision for a single, ubiquitous wireless communication standard throughout the world. Ø The following table illustrates the primary worldwide proposals that were submitted for IMT-2000 in Two of these proposals, i.e. CDMA2000 and W- CDMA, take the lead. With major political and economic backing behind both camps (techno-politics!), the hope for a single worldwide standard did not come true, at least within the 3G era. Ø The world s first 3G commercial system was launched by SK Telecom (Korea) in October It is based on CDMA2000. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

27 Third Generation (3G) Cellular Systems (cont d) For more information, check O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

28 Non-Cellular Wireless Access Systems Wireless Local Area Networks (WLANs) License-free, low-power, short-range data communications Wi-Fi (IEEE a/b/g/n) Wireless Metropolitian Area Networks (WMANs) Last-mile brodband access Wi-Max (IEEE e/d), WiBro (Korea), HIPERMAN (Europe) Wireless Personal Area Networks (WPANs) Interdevice connection within the range of a person/home Bluetooth, Zigbee (IEEE ) O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

29 Wireless Metropolitan Area Networks (WMANs) Ø Fixed wireless access provides a reliable and inexpensive alternative to fiber optic for the last mile. Ø Unlike mobile cellular phone systems, fixed wireless access systems are able to take the advantage of time-invariant nature between the fixed transmitter and the fixed receiver. Ø Standardization efforts are centered around IEEE and ETSI-HiperMAN. Ø For updated information, check O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

30 Wireless Local Area Networks (WLANs) Ø WLANs provide license-free, low-power short-range data communications, which facilitates internet connection and private computer communications at the workplace and other designated areas such as coffee shops, airports, libraries, etc. as well as for home-networking. Ø Although the IEEE WLAN standard body was established in 1987, WLAN did not get popular until recently. The large scale acceptance of Internet combined with increasing use of laptop and other mobile computing devices such as smart phones has caused WLAN to get further momentum. Ø WLANs operate in the 2.4 GHz ISM (Industrial, Scientific and Medical) band. These are the same unlicensed bands where cordless phones, baby monitors and Bluetooth devices operate. Ø Current WLAN standards are based on IEEE a/b/g/n. Although the term Wi-Fi has been originally introduced to denote b, it is currently used as a generic term. Check for latest updates. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

31 Wireless Personal Area Networks (WPANs) Bluetooth Ø Named after King Harald Bluetooth (the 10th century Viking who united Denmark and Norway), the Bluetooth standard aims to unify the connectivity chores of appliances within the personal workspace of an individual. Ø Bluetooth is an open standard that has been embraced by over 1000 manufacturers of electronic appliances. It provides an ad-hoc approach for enabling various devices to communicate with one another within a typical 10 meter range. It operates in the unlicensed 2.4 GHz ISM band. Ø For further information, check O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

32 LTE and 4G and beyond Ø The basic technology driver: Higher and higher data rates to support everincreasing demands of end-users (smart phone data hungry apps, augmented reality, social networks, video streaming and gaming, etc). Ø Goal: 100 Mbps for high mobility users and 1Gbps for low mobility wireless users. Ø 4G should not be seen as a linear extension of 3G cellular: Seamless service provisioning across a multitude of wireless systems/ platforms à Heterogeneous networks Ø A single, ubiquitous seamless cellular phone standard (if techno-politics allows): You will be able to use your cellular phone wherever you go all over the world. O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

33 Where wireless is heading Integration of Systems/Standarts Multimode 4G devices (A current example: Cell phones switching between Wi-Fi and cellular are already in the market) O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

34 Expectations from 4G 4G is envisioned to Support peak rates of 100Mbit/s for mobile and 1Gbit/s for nomadic and pedestrian situations (Ref: Support cost-effective solutions from the end-user perspective (under the assumption that subscribers will not be willing to pay the same amount per data bit as for voice bit ) Support high QoS (better reception, less dropouts, clearer voice calls) and energy efficiency (longer battery life) Support spectral-efficient solutions (bandwidth is expensive!) Support cost-effective solutions (e.g., base station density, infrastructure cost) from the operator perspective considering that subscriber numbers tend to saturate in developed countries O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter

35 HSPA (HighSpeed Packet Access ) Specifications Data rates up to 14Mbps in the downlink and 5.8Mbps in the uplink HSPA improvements in UMTS spectrum efficiency are achieved through: New modulation techniques (16QAM and 64QAM ) Reduced radio frame lengths New functionalities within radio networks (e.g. Fast retransmission ) Consequently, throughput is increased and latency is reduced MIMO capability coupled with improvements in the radio access network for continuous packet connectivity, HSPA+ allows Uplink speeds of 11Mbps and Downlink speeds of 42Mbps Dual cell or Dual carrier HSPA was defined in 3GPP Release 8, specifying carrier aggregation for increased spectrum efficiency and load balancing across the carriers

36 4G Specifications LTE-Advanced is one the candidates. The following features are supported in LTE-Advanced proposals: Enhanced uplink multiple access with OFDMA. Higher order MIMO transmission. Up to 8x8 MIMO in the downlink and 4x4 MIMO in the uplink is used to reach peak data rates. Beamforming with spatial multiplexing is being considered to increase data rates, coverage, and capacity. Coordinated multipoint (CoMP) transmission and reception. This MIMO variant is intended to improve performance for high data rates, cell edge throughput, and system throughput. Relaying: receive, amplify, and retransmit downlink and uplink signals to improve coverage.

37 What shall we see in this course Characterization of the propagation channel (Chapter 2) Bandpass signaling techniques (Chapter 3) Diversity (Chapter 4) Fundamentals of cellular communications (Chapter 5) Multiple access techniques (Chapter 6) O. Damen, ECE414 Wireless Communications, University of Waterloo, Winter