April 25, 2005Topic 5 1 Telecommunications Engineering Topic 5: Wireless Architectures James K Beard, Ph.D.

Topic 52 April 25, 2005 Essentials Text: Simon Haykin and Michael Moher, Modern Wireless Communications SystemView  Use the full version in E&A 603A for your term project Web Site  URL  Content includes slides for EE320 and EE521  SystemView page  A few links Office Hours  E&A 349  Hours Tuesday afternoons 3:00 PM to 4:30 PM  MWF 10:30 AM to 11:30 AM  Others by appointment; ask by

Topic 53 April 25, 2005 Topics Architecture topics  Open System Interconnection (OSI) model  Power control  Handover  The Network Layer Other areas from earlier chapters are reviewed

Topic 54 April 25, 2005 Open System Interconnection (OSI) Model Seven-layer model  Physical layer (modem)  Data link layer  Network layer  Transport layer (packetizing, ACK/NAK)  Session layer (Service selection and access)  Presentation layer (encryption, compression)  Application layer (HMI) Layers designed together as a system

Topic 55 April 25, 2005 Example 7.1: and the Seven-Layer Model Application layer – client software Presentation layer – compression and encryption (SSH) Session layer – interface with host Transport layer – TCP interface, IP addressing Network layer – routing, adds header Data link layer – adds header and addresses of host, adds CRD bits; medium access layer (MAC) selects free channel and passes to… Physical layer – FEC and modulation, yet another header

Topic 56 April 25, 2005 Power Control Architectures Open Loop  Mobile terminals measure strength of pilot channel  Transmit power decreased for strong pilot channels  Fast and simple, but must be approximate Closed Loop  Base station measures mobile terminal signal strength  Mobile station receives signal strength by downlink  Accurate but delay and averaging must be smaller than channel coherence time Outer Loop Control  Base station uses expected signal strength in control algorithm  Complexity can result in a slow loop

Topic 57 April 25, 2005 Power Control: Summary Power control minimizes SINR in busy cells Handset power control minimizes SINR in the base station but not at the mobile terminal Methods still evolving Next generation standards will implement  Newer techniques such as outer-loop control  Base station power control for SINR control at the mobile station

Topic 58 April 25, 2005 Example 7.3: The Near-Far Problem Mobile terminal distance to base station varies from 100 m to 10 km Power differences  Given a path loss exponent of 4  Difference in received power at base station is 80 dB Spreading rate of 128 million required to prevent jamming of weaker user Solution is power control

Topic 59 April 25, 2005 Handover Issues Purpose  Address operational transition of mobile terminals between cells  Maintain continuity of calls Calls are dropped in handover because  Mobile station signal strength drops too low before handover is completed  The new cell doesn’t have a free channel

Topic 510 April 25, 2005 Handover Techniques Start handover when signal strength is decreasing but a margin still exists  Common technique with first-generation systems  Margin can be small with second-generation systems that switch cells quickly Mobile assisted  Use base station signal strength in handover logic  Avoids cell dragging in which mobile station operates well into another cell, and causes interference with other mobile stations

Topic 511 April 25, 2005 Handover Multiple-Access Issues FDMA and TDMA  Mobile station must change signaling channels and traffic channels in handover  Called hard handover CDMA  Signaling channels are the same during handover  Called soft handover SDMA  Switch stations when mobile station transitions between beam boundaries  Can become complex when base station tracks users with steerable beams

Topic 512 April 25, 2005 The Network Layer Components Base station  RF links to mobile terminals  RF, wire, fiber or other links to mobile switching center Switching Center  Handles billing and authorization  Executes interconnects between base stations, other networks, or land line telecommunications

Topic 513 April 25, 2005 Mobile Switching Center Functions Billing and authorization  Counts the minutes  Determines roaming status and finds home station/account  Rings the cash register  Modifies routing where appropriate Interface between cellular and public land line telephone networks Overall supervision of mobile access control (MAC) wireless communications network  Power control functions  Handover  Provide data capability to mobile terminals

Topic 514 April 25, 2005 Indoor LANs Terminology  Cells are service sets  User terminals are stations  Base stations are stations Peculiarities  Often design and growth is ad hoc without planning  Dissimilar packet sizes through network  Wired and terminals on same station

Topic 515 April 25, 2005 Physical Layer for Various MAC Standards (Table 7.2 p. 470)

Topic 516 April 25, 2005 Physical Layer for Various Data Network Standards (Table 7.3)

Topic 517 April 25, 2005 Theme Example 5: (Wi-Fi) Pages Timeline  User station (STA) logs onto local base station (AP), AP authenticates STA and provides ID  STA listens Inactive channel – STA sends RTS, AP sends CTS Active channel – listens for gap and sends packet  STA fragments and sends packet  AP reassembles packet and sends to network layer  AP disassembles packet from network layer and sends to STA Random time access (like Ethernet)

Topic 518 April 25, 2005 (5)(7) Convolutional Code with Hard Decoding

Topic 519 April 25, 2005 (5)(7) Convolutional Code with Soft Decoding

Topic 520 April 25, 2005 Problem 2.59 Page 102 When G. Marconi made the first radio transmission in 1899 across the Atlantic Ocean, he used all of the spectrum available worldwide to transmit a few bits per second. It has been suggested that, in the period since then, spectrum usage (bits/s/Hz worldwide) has increased by a factor of a million. List the factors that have resulted in this substantial increase. Which factor will likely result in the largest increase in the future?

Topic 521 April 25, 2005 Factors That Increase Spectral Usage

Topic 522 April 25, 2005 Problem 3.2 Page 110 Consider the sinusoidal modulating signal Show that the use of double sideband, suppressed carrier (DSB-SC) modulation produces a pair of side frequencies, one at f c +f m and the other at f c -f m, where f c is the carrier frequency. What is the condition that the modulator has to satisfy in order to make sure that the two side-frequencies do not overlap?

Topic 523 April 25, 2005 Solution for Problem 3.2

Topic 524 April 25, 2005 Polynomial Arithmetic Modulo 2 Integer arithmetic modulo 2  Add, subtract, multiply integers  Take this result modulo 2  Solution is always 0 or 1  Division? Reciprocal of odd numbers is 1 Polynomial arithmetic modulo 2  Integers are coefficients of polynomials  Perform polynomial arithmetic as usual  Take coefficients of result modulo 2

Topic 525 April 25, 2005 Examples Two polynomials Multiplying them Taking the result modulo 2

Topic 526 April 25, 2005 Finite Fields Example  Integer arithmetic modulo 7  Elements are {0,1,2,3,4,5,6}  Reciprocals pairs are (1,1), (2,4), (3,5), (6,6)  Division is defined as multiplication by reciprocal All integer arithmetic modulo a prime defines a finite field

Topic 527 April 25, 2005 Vector Extensions of Finite Fields Sometimes called polynomial fields or Galois fields The exist for orders N equal to any power k of a prime p: N=p k Arithmetic  Elements are characterized as the coefficients of a polynomial of order k-1  Addition and subtraction is done modulo p  Multiplication is defined as modulo a generating polynomial of order k

Topic 528 April 25, 2005 Defining Characteristics of Galois Fields Successive multiplication by x  Begin with 1  Steps through all N elements except zero  A sequence of length N-1 A reciprocal  Defined as producing 1 as a product  Always exists Division is defined as multiplication by reciprocal

Topic 529 April 25, 2005 Special Case for Signal Processing Galois fields of order 2 k The series of coefficients is a sequence of k zeros and ones Addition and subtraction  Are identical operations in this field  Result is a bit-by-bit XOR Multiplication  Modulo a generating polynomial of order k  Generating polynomial can be added or subtracted  Table 5.1 page 272 lists some generating polynomials

Topic 530 April 25, 2005 Generation with Shift Registers Basis is a shift register with k latches Shifting is equivalent to multiplication by x A 1 shifted out  Fed back in according to the 1s in the generating polynomial  Addition is done with an XOR

Topic 531 April 25, 2005 Example Generating Polynomial:

Topic 532 April 25, 2005 Definitions of Orthogonality Vectors with arithmetic modulo 2  Addition of two orthogonal vectors gives the zero vector  A set of vectors that is closed on addition has the properties Sum of any two is another in the set The zero vector is always included  A basis set has the property Sum of any two is never another in the basis set or zero The opposite of closed on addition Orthogonal signals

Topic 533 April 25, 2005 Next Time Assignment:  Look at the study guide  Go over the slides to date  Look particularly at Chapters 4 and 7  Make up a list of questions  Send them to me by