Wireless and going mobile

Browsing via low energy photons

Radio Basics

Radio power fades as 1/distance^2 from where it’s transmitted.

Power needed is proportional to bandwidth.

Range and bandwidth limited by noise. Signals can bounce causing multipath. Low frequency signals can go around

things.

Modulation

Information carried by changing a radio signal, or carrier. Can change frequency (FM) Can change Amplitude or Strength

(AM) There are lots of complex

modulation schemes.

Point to Point Communication One radio transmits signals to the

other Can enable (transmit) its carrier all

the time, or part of the time Can have one radio Rx on one

frequency, Tx on another (duplex) Can share one frequency (simplex)

Multipoint Communication One radio talks to a bunch of other

radios. Need to share frequencies, control

access to radio waves Need to address communication to

correct radios Like Ethernet!

Cell phones!

Lots of cells covering region Reduces range to radios Increase bandwidth Decreases power needed in radio.

Cells linked together by communication links, and back to phone system.

Cellular systems

AMPS (Advanced Mobile Phone Service): Not so advanced. Analog sound transmitted over radio waves with some digital data. Works by using different frequencies for users.

TDMA (Time Division Multiplexed Access): Constantly rotate between different users. Each gets a different time slot.

More Cellular systems!

GSM (Global System for Mobile Comms): Yet another TDMA! Narrowband TDMA -- multiple frequencies, with time division, 8 channels, on top. LOTS of data capability.

CDMA (Code Division Multiple Access): Spread spectrum comms! Constantly hops from one frequency to another. Very efficient!

Wireless Ethernet

Ethernet packets broadcast over a radio channel

Can have a Point to Point network connection: like a wireless CAT-5 cable.

Often want multipoint network: more like a bunch of nodes on a network. Need to share system.

Sharing the radio waves

Frequency Hopping (FH): Jump occasionally. 75 or more frequencies used. Up to 2 Mbps.

Digital Sequential Spread Spectrum (DSSS): Jumping frequency LOTS of times per second. Can go way faster. Needs way more power.

DSSS

Doesn’t use frequency very efficiently

Needs more radios - more cells Has some resistance to multipath.

Good range. Works by actually transmitting a far

higher bandwidth signal than the data!

The new kid in town - OFDM Orthogonal Frequency Division

Multiplexing Stuff the frequencies used as close

as physics allows Channels actually overlap, but can

be separated by complex math done by the radio.

Needs really good radios to make it work.

OFDM rules! Extremely multipath independent.

Considered to be effectively non-line-of-site, if used at enough power. Can use bounces, not just resist them.

In principle, can be low power, once made small enough.

Fourth Generation (4G) communications, including cell phones.

Darned fast!!!! 30 Mbps or more! Mars!

Wireless networking

Access point connected to the network

Wireless cards in computers, or computers hooked to other access points.

Access point controls communication over network.

Roaming on ethernet IEEE 802.11, the ethernet wireless

standard (WiFi): Defines basic radio communication

methods. DSSS primarily used so far. Defines how to make the radio links

secure: Wired-Equivalent Privacy. Defines how to move from one

access point to another Cells!

The Network, everywhere As wireless systems start to

appear everywhere, we’ll need far more advanced networks to deal with issues: Who can access the network How to allocate IP numbers How to access users services back

home

IPv6, the next generation Internet! WAY larger address space: 128

bits instead of 32! 16 numbers! 2 x 10^20 addresses per square

cm of land on Earth! Address split into pieces: local

address and global address. Automatic allocation of addresses

is mandatory. No manual setting of local addresses.

Die NAT Die!

Network Address Translators: convert local addresses to just one address on the outside. Simple firewall. Share IP numbers.

New protocols cannot operate through NAT, as it’s very fixed.

IPv6 gets away from needing NAT.

Local Address

Built from a unique address, usually the ethernet address

Something like fe80::240:12ce:c3a0:80. Lower 64 bits are local

Unique identification of machine.

Mobile IP Don’t confuse with Mobile Internet

(which is about cellphones)! You plug your machine into a network Your machine sends a request back to

your home network giving it your local address

A “Mobile Agent” transmits network packets back from your network to wherever you are in the local network. Local net in upper part of address.

The network of tomorrow You’ll just access a network Your identity, and permission to use

the local network, will be verified. You’ll see your services from your

home network, and from other locations on the network.

You’ll never need to program in your IP number.

The network will be everywhere.