Wireless CommunicationLecture 1: Introduction to Wireless RF Propagation and

Wireless Networks

Frequency Allocation

Usage of Frequency Bands

Spectrum Allocation for WLANs

Allocation of Frequency Bands for Cellular Communication

Current / Planned Technologies Band Frequency (MHz)

SMR iDEN, ESMR CDMA 800 806-824 and 851-869

AMPS, GSM, IS-95 (CDMA), IS-136 (D-AMPS), 3G Cellular 824-849 and 869-894

GSM, IS-95 (CDMA), IS-136 (D-AMPS), 3G PCS 1850–1910 and 1930–1990

3G, 4G, MediaFlo, DVB-H 700 MHz 698-806

Unknown 1.4 GHz 1392–1395 and 1432–1435

3G, 4G AWS 1710–1755 and 2110–2155

4G BRS/EBS 2496–2690

GSM General Info• GSM 900 uses the circa 900Mhz band• The frequency band used is 890-915MHz (mobile transmit) and 935-960MHz

(base transmit).• To allow maximum number of users access, each band is subdivided into 124

carrier frequencies spaced 200 kHz apart, using FDMA techniques. • Each of these carrier frequencies is further subdivided into time slots using TDMA

.• TDMA (Time Division Multiple Access) has 8 time slots (i.e. transmitting for one

eighth of the time). • Hence, one radio channel can support 8 'full rate' traffic. • A more economical 'half rate' scheme with 16 traffic channels is being

introduced. • TDMA provides each user with the carrier frequency for approximately 0.577ms. • There is also an extension band of 15 MHz in both directions. • The peak power of mobile stations depends on the class of mobile.

GSM General Info• Precautions are required to avoid Interference with other users. Power

control - 15 steps of 2dB - is provided. The transmitter must be ramped up and down in level in a controlled fashion at the beginning and end of each time slot.

• Frequency hopping may be optionally employed in order to avoid 'deadspots' and to minimize interference from other signals. The hopping rate is one hop per TDMA frame (4.6µs), or 217 hops per second.

• The method of modulation used Is Gaussian Minimum Shift Keying (GMSK)at a gross data rate of 270 kb/s.

• Phase and frequency synchronization must allow for Doppler shift for vehicle speeds up to 250km/h as well as for frequency standard drift, and timing advance to compensate for propagation delay due to round trips for paths, in cells up to 35km radius.

GSM Mobile Phone Classes

• Class II (8 Watts)• Class III (5 Watss)• Class IV (2 Watts)• Class V (0.8 – 2 Watts)

Some Buzzwords

• 2G (Second Generation)

• 2.5G (Interim GSM Generation before 3G, after 2G - GPRS)

• GPRS (General Packet Radio Service)

• 3G (Third Generation)

• IMT-2000 (International Mobile Telecommunications 2000)

• UMTS (Universal Mobile Telephony System)

• CDMA (Code Division Multiple Access)

• W-CDMA (Wideband CDMA)

• FOMA (Freedom of Mobile Multimedia Access)

• cdma2000

Evolution of Cellular Technology• 3G (Third Generation) is a generic name for a set of mobile

technologies which uses a host of high-tech infrastructure networks, handsets, base stations, switches and other equipment to allow mobiles to offer high-speed Internet access, data, video and CD-quality music services. Data speeds in 3G networks should be up to 2 Mbps, an increase on current technology.

• :: 2G/2.5G DefinedGSM for example is a 2G technology. It uses TDMA technology, proving data speeds of 9.6kbps/14.4kbps. The packet radio upgrade to GSM, called GPRS, can have speeds of up to 114kbps. GPRS an interim technology towards 3G, and hence is known as 2.5G. GSM might go the same way as the older first generation AMPS networks in 8-15 years because of the use of newer and better UMTS technology

CDMA

• The new 3G services are almost all flavours of technologies based on the generic name, CDMA (Code Division Multiple Access). CDMA is a digital wireless technology that allows multiple users to share radio frequencies at the same time without interfering with each other. A voice or data call is assigned a unique code that distinguishes it from others and since the signals hop among different frequencies.

• Current 2G services using the original CDMA "IS-95" technology are known as cdmaOne. 3G services will use new high-speed versions of CDMA called W-CDMA, or its competing technology,

IMT-2000

• IMT-2000 (International Mobile Telecommunications 2000). When the ITU tried to unify and standardise 3G technologies, no consensus was reached. There were thus five terrestrial standards developed as part of the IMT-2000 program. Instead, depending on where in the world 3G will be implemented, the 3G standard is based on CDMA variants cdma2000 or W-CDMA.

IMT-2000The primary CDMA variants that are used in IMT-2000 3G networks are W-CDMA (Wideband CDMA) and cdma2000, which are similar but not the same, so that W-CDMA handsets will not work with cdma2000 handsets and visa versa.

W-CDMA (Wideband CDMA)W-CDMA is the competitor to cdma2000 and one of two 3G standards that makes use of a wider spectrum than CDMA and therefore can transmit and receive information faster and more efficiently. Co-developed by NTT DoCoMo, it is being backed by most European mobile operators and is expected to compete with cdma2000 to be the de facto 3G standard

• UMTS (W-CDMA)In Europe, 3G W-CDMA networks are known as UMTS (Universal Mobile Telephony System) another name for w-CDMA/3G services. Governments in the region held UMTS auctions for 3G licences netting $108 billion in 2000.

• FOMA (W-CDMA)Japanese giant NTT DoCoMo Inc brand name for 3G services is FOMA (Freedom of Mobile Multimedia Access) and is based on the W-CDMA format

CDMA2000• Then there is cdma2000, the other 3G standard. It is the upgarde to

cdmaOne. It can use of a wider spectrum than CDMA and therefore can transmit and receive information faster and more efficiently, making fast Internet data, video, and CD-quality music transmission possible. There are however new cdma2000 variants called cdma2000 1X, 1X-EV-DV, 1X EV-DO, and cdma2000 3X. They deliver 3G services while occupying a very small amount of current spectrum (1.25 MHz per carrier) as opposed to UMTS which requires completely NEW spectrum (hence the auctions).

• That is why cddma2000 is considered slightly more technologically advanced than the competing W-CDMA standard. CDMA2000 is not constrained to only the IMT band; it is defined to operate in existing cellular and PCS spectrum as well as IMT spectrum, thereby maximizing flexibility for operators. Cdma2000 is expected to be compatible with CDMA and GSM/TDMA networks so that GSM networks can "overlay" a cdma2000 network over their GSM networks.

CDMA2000

1X• CDMA2000 1X (IS-2000), also known as 1x and 1xRTT, is the core

CDMA2000 wireless air interface standard. The designation "1x", meaning 1 times Radio Transmission Technology, indicates the same radio frequency (RF) bandwidth as IS-95: a duplex pair of 1.25 MHz radio channels. 1xRTT almost doubles the capacity of IS-95 by adding 64 more traffic channels to the forward link, orthogonal to (in quadrature with) the original set of 64. The 1X standard supports packet data speeds of up to 153 kbit/s with real world data transmission averaging 60–100 kbit/s in most commercial applications. IMT-2000 also made changes to the data link layer for greater use of data services, including medium and link access control protocols

CDMA20001xEV-DO

• CDMA2000 1xEV-DO (Evolution-Data Optimized), often abbreviated as EV-DO or EV, is a telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. It uses multiplexing techniques including code division multiple access (CDMA) as well as time division multiple access (TDMA) to maximize both individual user's throughput and the overall system throughput. It is standardized by 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and has been adopted by many mobile phone service providers around the world – particularly those previously employing CDMA networks. It is also used on the Globalstar satellite phone network.

HSDPA

• High-Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third generation) mobile telephony communications protocol in the High-Speed Packet Access (HSPA) family, also dubbed 3.5G, 3G+ or turbo 3G, which allows networks based on Universal Mobile Telecommunications System (UMTS) to have higher data transfer speeds and capacity. Current HSDPA deployments support down-link speeds of 1.8, 3.6, 7.2 and 14.0 Mbps. Further speed increases are available with HSPA+, which provides speeds of up to 42 Mbps downlink and 84 Mbps with Release 9 of the 3GPP standards.

Useful Link

• For a comprehensive list of Data Rates offered by different Communication (Wired and Wireless) Technologies, refer to

http://en.wikipedia.org/wiki/List_of_device_bandwidths

Addition of Sinusoids

Addition of Sinusoids

• The period of the total signal is equal to the period of the fundamental frequency. The period of the component sin (2πft) is equal to T = 1/f and the period of s(t) is also T.

• The second frequency is an integer multiple of the first frequency. When all of the frequency components of a signal are integer multiples of one frequency, the latter frequency is referred to as the fundamental frequency.

Multiplication of Sinusoids • What happens when we multiply a low frequency sinusoids with a

higher frequency sinusoid? Begin by using the inverse Euler formula:

which is a sum of real sine functions.

Sinusoidal multiplication can therefore be expressed as an addition (which makes sense because all signals can be represented by the sum of sinusoids).

Spectrum and Bandwidth• The spectrum of a signal is the range of frequencies that it contains. For the

signal of previous figure (third waveform), the spectrum extends from f to 3f. The absolute bandwidth of a signal is the width of the spectrum. In the case of the previous figure (third waveform) , the bandwidth is 2f. Many signals, such as that of a square pulse have an infinite bandwidth.However, most of the energy in the signal is contained in a relatively narrowband of frequencies. This band is referred to as the effective bandwidth, or justbandwidth.One final term to define is dc component. If a signal includes a component ofzero frequency, that component is a direct current (dc) or constant component. For example, the figure on the next slide shows the result of adding a dc component to the signal of previous figure (third waveform). With no dc component, a signal has an average amplitude of zero, as seen in the time domain. With a dc component, it has a frequency term at and a nonzero average amplitude.

Sinusoids with a DC Component

Frequency Domain Representation of a Square Wave

Reducing the Time Period of the Square Wave

As the fundamental period of the time waveform increases, the fundamental frequency of the Fourier series components making up the waveform decreases and the harmonics become more closely spaced.

Approximating a Square Wave

Frequency components of the square wave with amplitudes A and –A can be given as:

Consider a square wave in which we let a positive pulse represent binary 0 and a negative pulse representbinary 1. Then the waveform represents the binary stream 0101. . . . The duration of each pulse is 1/(2f); thus the data rate is 2f bits per second (bps).

Some Bandwidth ConsiderationsSuppose that we are using a digital transmission system that is capable of transmitting signals with a bandwidth of 4 MHz. Let us attempt to transmit a sequence of alternating 1s and 0s as the square wave of Previous figure (Case 3).What data rate can be achieved? We look at three cases.

Case I. Let us approximate our square wave with the waveform of Previous Figure (Case 1).Although this waveform is a “distorted” square wave, it is sufficiently close to the square wave that a receiver should be able to discriminate between a binary 0 and a binary 1. If we let f = 106 cycles/second = 1 MHz then the bandwidth of the signal

Bandwidth Considerations Case II. Now suppose that we have a bandwidth of 8 MHz. Let us look again atPrevious Figure (First Case), but now with f = 2 MHz. Using the same line of reasoning as before, the bandwidth of the signal is (5 * 2 * 106) – (2 * 106) = 8 MHz. But in this caseT = 1/f = 0.5 μs. As a result, one bit occurs every 0.25 μs for a data rate of 4 Mbps. Thus, other things being equal, by doubling the bandwidth, we double the potential data rate.Case III. Now suppose that the waveform of Figure below is considered adequate for approximating a square wave. That is, the difference between a positive andnegative pulse is sufficiently distinct that the waveform can be successfully used to represent a sequence of 1s and 0s. Assume as in Case II that f = 2 MHz and T = 1/f = 0.5 μs so that one bit occurs every 0.25 μs for a data rate of 4 Mbps. Using the waveform of Figure below, the bandwidth of the signal is (3 * 2 * 106) – (2 * 106) = 4 MHz. Thus, a given bandwidth can support various data rates depending on the ability of the receiver to discern the difference between 0 and 1 in the presence of noise and other impairments.

Bandwidth and Data Rate

Figure on the left shows a digital bit stream with a data rate of 2000 bits per second. With a bandwidth of 2500 Hz, or even 1700 Hz, the representation is quite good. Furthermore, we can generalize these results. If the data rate of the digital signal is W bps, then a very good representation can be achieved with a bandwidth of 2W Hz. However, unless noise is very severe, the bit pattern can be recovered with less bandwidth than this. Thus, there is a direct relationship between data rate and bandwidth: The higher the data rate of a signal, the greater is its required effective bandwidth.Looked at the other way, the greater the bandwidth of a transmission system, the higher is the data rate that can be transmitted over that system.

Adding Sinusoids with different phases

• If two sinusoids are `in phase' then their peaks and troughs coincide and the result is as observed earlier. If the sinusoids are `out of phase' or in other words if they differ in phase by π radians then their peaks and troughs oppose each other and they will cancel each other out. The phase of the resulting sinusoid is the sum of the phases of the constituents.

• When a number of different frequencies are combined the frequency of the result will in general be that of the lowest frequency component. This is often called the fundemental frequency of the signal.

Representation of Signals

• With time domain representation we can see the amplitude variation of the composite signal.

• With the frequency domain representation, we can see the amplitude of each constituent frequency component. Therefore the effect of impairments in the wireless medium can be seen by calculating the frequency response of the channel.

• The time period of the composite signal is equal to the time period of its fundamental frequency.

General Info

• It can be shown, using Fourier analysis, that any signal is made up of components at various frequencies, in which each component is a sinusoid. By adding together enough sinusoidal signals, each with the appropriate amplitude, frequency, and phase, any electromagnetic signal can be constructed. Put another way, any electromagnetic signal can be shown to consist of a collection of periodic analog signals (sine waves) at different amplitudes, frequencies, and phases.

Cisco’s Three Layer Hierarchical model

Core LayerThe core layer is responsible for fast and reliable transportation of data across a network. The core layer is often known as the backbone or foundation network because all other layers rely upon it. Its purpose is to reduce the latency time in the delivery of packets. The factors to be considered while designing devices to be used in the core layer are: High data transfer rate: Speed is important at the core layer. One way that core networks enable high data transfer rates is through load sharing, where traffic can travel through multiple network connections.

Low latency period: The core layer typically uses high-speed low latency circuits which only forward packets and do not enforcing policy. High reliability: Multiple data paths ensure high network fault tolerance; if one path experiences a problem, then the device can quickly discover a new route.

• At the core layer, efficiency is the key term. Fewer and faster systems create a more efficient backbone. There are various equipments available for the core layer:

T-1 and E-1 lines, Frame relay connections, ATM networks, Switched Multimegabit Data Service (SMDS), DWDM, WDM etc

Distribution LayerThe distribution layer is responsible for routing. It also provides policy-based network connectivity, including: Packet filtering (firewalling): Processes packets and regulates the transmission of packets based on its source and destination information to create network borders.

• QoS: The router or layer 3 switches can read packets and prioritize delivery, based on policies you set.

• Access Layer Aggregation Point: The layer serves the aggregation point for the desktop layer switches.

• Control Broadcast and Multicast: The layer serves as the boundary for broadcast and multicast domains.

• Application Gateways: The layer allows you to create protocol gateways to and from different network architectures.

• The distribution layer also performs queuing and provides packet manipulation of the network traffic.

• It is at this layer where you begin to exert control over network transmissions, including what comes in and what goes out of the network. You will also limit and create broadcast domains, create virtual LANs, if necessary, and conduct various management tasks, including obtaining route summaries. In a route summary, you consolidate traffic from many subnets into a core network connection.

Access LayerThe access layer contains devices that allow workgroups and users to use the services provided by the distribution and core layers. In the access layer, you have the ability to expand or contract collision domains using a repeater, hub, or standard switch. In regards to the access layer, a switch is not a high-powered device, such as those found at the core layer.

Rather, a switch is an advanced version of a hub.

A collision domain describes a portion of an Ethernet network at layer 1 of the OSI model where any communication sent by a node can be sensed by any other node on the network. This is different from a broadcast domain which describes any part of a network at layer 2 or 3 of the OSI model where a node can broadcast to any node on the network.

At the access layer, you can: Enable MAC address filtering: It is possible to program a switch to allow only certain systems to access the connected LANs.

• Create separate collision domains: A switch can create separate collision domains for each connected node to improve performance.

• Share bandwidth: You can allow the same network connection to handle all data.• Handle switch bandwidth: You can move data from one network to another to perform load

balancing.

Challenges

• Network Challenges– Scarce spectrum– Demanding/diverse applications– Reliability– Ubiquitous coverage– Seamless indoor/outdoor operation– Application Demand based handovers

• Device Challenges– Size, Power, Cost– Multiple Antennas in Silicon– Multiradio Integration – Coexistance

Cellular

AppsProcessor

BT

MediaProcessor

GPS

WLAN

Wimax

DVB-H

FM/XM

Evolution of Current Systems

• Wireless systems today– 3G Cellular: ~200-300 Kbps.– WLANs: ~450 Mbps (and growing).

• Next Generation is in the works– 4G Cellular: OFDM/MIMO– 4G WLANs: Wide open, 3G just being finalized

• Technology Enhancements – Hardware: Better batteries. Better circuits/processors.– Link: More bandwidth, more antennas, better modulation and coding,

adaptivity, cognition.– Network: better resource allocation, cooperation, relaying,

femtocells.– Application: Soft and adaptive QoS.

Multimedia Requirements

Voice VideoData

Delay

Packet Loss

BER

Data Rate

Traffic

<100ms - <100ms

<1% 0 <1%

10-3 10-6 10-6

8-32 Kbps 10-1000 Mbps 10-1000 Mbps

Continuous Bursty Continuous

One-size-fits-all protocols and design do not work wellWired networks use this approach, with poor results

Quality-of-Service (QoS)

• QoS refers to the requirements associated with a given application, typically rate and delay requirements.

• It is hard to make a one-size-fits all network that supports requirements of different applications.

• Wired networks often use this approach with poor results, and they have much higher data rates and better reliability than wireless.

• QoS for all applications requires a cross-layer design approach.

Crosslayer Design

• Application• Network

• Access• Link• Hardware

Delay ConstraintsRate Constraints

Energy Constraints

Adapt across design layersReduce uncertainty through scheduling

Provide robustness via diversity

Current Wireless Systems

• Cellular Systems• Wireless LANs• Wimax• Satellite Systems• Paging Systems• Bluetooth• Zigbee radios

4G/LTE/IMT Advanced

• Much higher peak data rates (50-100 Mbps)• Greater spectral efficiency (bits/s/Hz)• Flexible use of up to 100 MHz of spectrum• Low packet latency (<5ms).• Increased system capacity• Reduced cost-per-bit• Support for multimedia

Wifi NetworksMultimedia Everywhere, Without Wires

802.11n++

Wireless HDTVand Gaming

• Streaming video• Gbps data rates• High reliability• Coverage in every room

Wireless LAN Standards

• 802.11b (Old – 1990s)– Standard for 2.4GHz ISM band (80 MHz)– Direct sequence spread spectrum (DSSS)– Speeds of 11 Mbps, approx. 500 ft range

• 802.11a/g (Middle Age– mid-late 1990s)– Standard for 5GHz band (300 MHz)/also 2.4GHz– OFDM in 20 MHz with adaptive rate/codes– Speeds of 54 Mbps, approx. 100-200 ft range

• 802.11n (Recently Approved)– Standard in 2.4 GHz and 5 GHz band– Adaptive OFDM /MIMO in 20/40 MHz (2-4 antennas)– Speeds up to 600Mbps, approx. 200 ft range– Other advances in packetization, antenna use, etc.

Many WLAN cards have all 3

(a/b/g)

What’s next? 802.11ab

Wimax (802.16)

• Wide area wireless network standard– System architecture similar to cellular– Called “3.xG” (e.g. Sprint EVO), evolving into 4G

• OFDM/MIMO is core link technology• Operates in 2.5 and 3.5 GHz bands – Different for different countries, 5.8 also used.– Bandwidth is 3.5-10 MHz

• Fixed (802.16d) vs. Mobile (802.16e) Wimax– Fixed: 75 Mbps max, up to 50 mile cell radius– Mobile: 15 Mbps max, up to 1-2 mile cell radius

Satellite Systems

• Cover very large areas• Different orbit heights

– GEOs (39000 Km) versus LEOs (2000 Km)

• Optimized for one-way transmission– Radio (XM, Sirius) and movie (SatTV, DVB/S) broadcasts– Most two-way systems struggling or bankrupt

• Global Positioning System (GPS) use growing– Satellite signals used to pinpoint location– Popular in cell phones, PDAs, and navigation devices

8C32810.61-Cimini-7/98

Bluetooth

• Cable replacement RF technology (low cost)• Short range (10m, extendable to 100m)• 2.4 GHz band (crowded)• 1 Data (700 Kbps) and 3 voice channels, up to 3

Mbps

• Widely supported by telecommunications, PC, and consumer electronics companies

• Few applications beyond cable replacement

IEEE 802.15.4/ZigBee Radios

• Low-Rate WPAN• Data rates of 20, 40, 250 Kbps• Support for large mesh networking or star clusters• Support for low latency devices• CSMA-CA channel access• Very low power consumption• Frequency of operation in ISM bands

Focus is primarily on low power sensor networks

Tradeoffs

ZigBee

Bluetooth

802.11b

802.11g/a

3G

UWB

Range

Rate

Power

802.11n

Spectrum Regulation

• Spectrum a scarce public resource, hence allocated• Spectral allocation in US controlled by FCC

(commercial) or OSM (defense)• FCC auctions spectral blocks for set applications.• Some spectrum set aside for universal use• Worldwide spectrum controlled by ITU-R• Regulation is a necessary evil.

Innovations in regulation being considered worldwide, including underlays, overlays, and cognitive radios

Spectral ReuseDue to its scarcity, spectrum is reused

BS

In licensed bands

Cellular, Wimax Wifi, BT, UWB,…

and unlicensed bands

Reuse introduces interference

Emerging Systems*

• 4th generation cellular (4G)– OFDMA is the PHY layer– Other new features and bandwidth still in flux

• Ad hoc/mesh wireless networks• Cognitive radios• Sensor networks• Distributed control networks• Biomedical networks

Design Issues

• Ad-hoc networks provide a flexible network infrastructure for many emerging applications.

• The capacity of such networks is generally unknown.

• Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.

• Crosslayer design critical and very challenging.

• Energy constraints impose interesting design tradeoffs for communication and networking.

Cognitive Radios

• Cognitive radios can support new wireless users in existing crowded spectrum– Without degrading performance of existing users

• Utilize advanced communication and signal processing techniques– Coupled with novel spectrum allocation policies

• Technology could – Revolutionize the way spectrum is allocated worldwide – Provide sufficient bandwidth to support higher quality and higher

data rate products and services

Wireless Sensor NetworksData Collection and Distributed Control

Energy (transmit and processing) is the driving constraint Data flows to centralized location (joint compression) Low per-node rates but tens to thousands of nodes Intelligence is in the network rather than in the devices

• Smart homes/buildings• Smart structures• Search and rescue• Homeland security• Event detection• Battlefield surveillance• Smart Grids

Energy-Constrained Nodes

• Each node can only send a finite number of bits.– Transmit energy minimized by maximizing bit time– Circuit energy consumption increases with bit time– Introduces a delay versus energy tradeoff for each bit

• Short-range networks must consider transmit, circuit, and processing energy.– Sophisticated techniques not necessarily energy-efficient. – Sleep modes save energy but complicate networking.

• Changes everything about the network design:– Bit allocation must be optimized across all protocols.– Delay vs. throughput vs. node/network lifetime tradeoffs.– Optimization of node cooperation.

Discussion• Channel Impulse response and Frequency

response• Wireless as Last Mile Access Technique• Routing in wired and wireless networks• Need for Error and Flow Control per link in

wireless• Licensing requirements for licensed bands

Useful Links

• http://www.3gpp2.org/• http://www.wimaxforum.org/• http://www.ngmn.org/• http://www.3gpp.org/• http://www.broadband-forum.org/• http://femtoforum.org/• http://www.gsacom.com• http://ieeexplore.ieee.org/Xplore/