Wi-Fi and BluetoothLaboratorio di El&Tel

Mauro Biagi

10/04/23 Caratterizzazione trasmissioni WCDMA Pagina 2

Outline

•Wi-Fi and 802.11

•Wi-Fi acquisition and setup

•Bluetooth features

•Bluetooth acquisition and setup

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Wi-Fi is primarily a local area networking (LAN) technology designed to provide in-building broadband coverage.Wi-Fi is based on IEEE 802.11 specification.

Wi-Fi stands for Wireless Fidelity. Wi-Fi is based on the IEEE 802.11 family of standards and is primarily a local area networking (LAN) technology designed to provide in-building broadband coverage.

Current Wi-Fi systems based on IEEE 802.11a/g support a peak physical-layer data rate of 54Mbps and typically provide indoor coverage over a distance of 100 feet.Wi-Fi has become the defacto standard for last feet broadband connectivity in homes, offices, and public hotspot locations. systems can typically provide a coverage range of only about 1,000 feet from the access point.

IEEE 802.11 means Wi-Fi

IEEE 802.11 means Wi-Fi

Wi-Fi offers remarkably higher peak data rates than do 3G systems, primarily since it operates over a larger 20MHz bandwidth but Wi-Fi systems are not designed to support high-speed mobility.

One significant advantage of Wi-Fi over WiMAX and 3G is the wide availability of terminal devices. A vast majority of laptops shipped today have a built-in Wi-Fi interface. Wi-Fi interfaces are now also being built into a variety of devices, including personal data assistants (PDAs), cordless phones, cellular phones, cameras, and media players.

Wi-Fi is Half Duplex: All Wi-Fi networks are contention-based TDD systems where the access point and the mobile stations all vie for use of the same channel. Because of the shared media operation, all Wi-Fi networks are half duplex.There are equipment vendors who market Wi-Fi mesh configurations, but those implementations incorporate technologies that are not defined in the standardsChannel Bandwidth:The WiFi standards define a fixed channel bandwidth of 25 MHz for 802.11b and 20 MHz for either 802.11a or g networks.

There are three most important items which makes Wi-Fi working in your laptop or desktop. These are:Radio SignalsWi-Fi Card which fits in your laptop or computer.Hotspots which create Wi-Fi Network.

Radio Signals: Radio Signals are the keys which make WiFi networking possible. These radio signals transmitted from Wi-Fi antennas are picked up by WiFi receivers such as computers and cell phones that are equipped with WiFi cards. Whenever a computer receives any of the signals within the range of a WiFi network which is usually 300 - 500 feet for antennas, the WiFi card will read the signals and thus create an internet connection between the user and the network without the use of a cord.Access points which consist of antennas and routers are the main source which transmit and receive radio waves.Antennas work stronger and have a longer radio transmission with a radius of 300-500 feet which are used in public areas while the weaker yet effective router is more suitable for homes with a radio transmission of 100-150 feet.

Radio

Wi-Fi componentsWi-Fi Cards:You can think WiFi card as being an invisible cord that connects your computer to the antenna for a direct connection to the internet.WiFi cards can be external or internal, meaning that if a WiFi card is not installed in your computer, you may purchase a USB antenna attachment and have it externally connect to your USB port, or have an antenna-equipped expansion card installed directly to the computer. For laptops, this card will be a PCMCIA card in which you insert to the PCMCIA slot on the laptop.Wi-Fi Hotspots: A Wi-Fi hotspot is created by installing an access point to an internet connection. The access point transmits a wireless signal over a short distance (typically covering around 300 feet). When a Wi-Fi enabled device, such as a Pocket PC, encounters a hotspot, the device can then connect to that network wirelessly.Most hotspots are located in places that are readily accessible to the public, like airports, coffee shops, hotels, book stores and campus environments. 802.11b is the most common specification for hotspots worldwide. The 802.11g standard is backwards compatible with .11b but .11a uses a different frequency range and requires separate hardware such as an a, a/g, or a/b/g adapter. The largest public Wi-Fi networks are provided by private internet service providers (ISPs) that charge a fee for users to connect to the internet.

IEEE 802.11xThe 802.11 standard is defined through several specifications of WLANs. It defines an over-the-air interface between a wireless client and a base station or between two wireless clients.There are several specifications in the 802.11 family:

802.11: This pertains to wireless LANs and provides 1- or 2-Mbps transmission in the 2.4-GHz band using either frequency-hopping spread spectrum (FHSS) or direct-sequence spread spectrum (DSSS).

802.11a: This is an extension to 802.11 that pertains to wireless LANs and goes as fast as 54 Mbps in the 5-GHz band. 802.11a employs the orthogonal frequency division multiplexing (OFDM) encoding scheme as opposed to either FHSS or DSSS.

DSSS and FHFrequency Hopping Spread Spectrum (FHSS): derived from military radio technology where it was designed to be inherently secure and reliable under adverse battle conditions. Divides the available 83.5 MHz spectrum (in most countries) into 79 (or 75) discrete 1 MHz channels (the 4.5 MHz left over provides a 'guard bands' at either end of the spectrum), the Radio then hops around these 1 MHz channels in a pseudo-random sequence, using a minimum of 75 frequencies every 30 seconds and using any single frequency for a max. of 400 milliseconds.

Direct Sequence Spread Spectrum (DSSS): designed originally by two vendors to increase the available speed on the wireless network. Divides the available 83.5 MHz spectrum (in most countries) into 3 wide-band 22 MHz channels. Uses an 11 bit spreading code to reduce the possible interference on signals in each wide-band channel

DSSS and FHDHSS which uses 22 MHz channels will always be faster that FHSS which uses 1 MHz channels both in the UNII/ISM bands. Though by using techniques such as channel bonding FHSS can be used to reach 3 - 5 Mb range. As a rule of thumb modulation techniques will give 0.5 to 2+ times the MHz in bit/s throughput. So a 22 MHz using CCK gives ~11Mb (0.5) throughput and using OFDM (11.g) with is giving 55Mb (2+).

IEEE 802.11x

802.11b: The 802.11 high rate Wi-Fi is an extension to 802.11 that pertains to wireless LANs and yields a connection as fast as 11 Mbps transmission (with a fallback to 5.5, 2, and 1 Mbps depending on strength of signal) in the 2.4-GHz band. The 802.11b specification uses only DSSS. Note that 802.11b was actually an amendment to the original 802.11 standard added in 1999 to permit wireless functionality to be analogous to hard-wired Ethernet connections.

802.11g: This pertains to wireless LANs and provides 20+ Mbps in the 2.4-GHz band.

IEEE 802.11 access

IEEE 802.11 wireless LANs use a media access control protocol called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). While the name is similar to Ethernet.s Carrier Sense Multiple Access with Collision Detection (CSMA/CD), the operating concept is totally different.Wi-Fi systems are half duplex shared media configurations where all stations transmit and receive on the same radio channel.

The fundamental problem this creates in a radio system is that a station cannot hear while it is sending, and hence it impossible to detect a collision.

Because of this, the developers of the 802.11 specifications came up with a collision avoidance mechanism called the Distributed Control Function (DCF).

According to DCF, A Wi-Fi station will transmit only if it thinks the channel is clear. All transmissions are acknowledged, so if a station does not receive an acknowledgement, it assumes a collision occurred and retries after a random waiting interval.

The incidence of collisions will increase as the traffic increases or in situations where mobile stations cannot hear each other.

IEEE 802.11 access

WiFi systems use two primary radio transmission techniques.802.11b (<=11 Mbps): The 802.11b radio link uses a direct sequence spread spectrum technique called complementary coded keying (CCK). The bit stream is processed with a special coding and then modulated using Quadrature Phase Shift Keying (QPSK).

802.11a and g (<=54 Mbps): The 802.11a and g systems use 64-channel orthogonal frequency division multiplexing (OFDM). In an OFDM modulation system, the available radio band is divided into a number of sub-channels, and some of the bits are sent on each.

The transmitter encodes the bit streams on the 64 subcarriers using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), or one of two levels of Quadrature Amplitude Modulation (16, or 64-QAM).

IEEE 802.11 rates

Some of the transmitted information is redundant, so the receiver does not have to receive all of the sub-carriers to reconstruct the information.The original 802.11 specifications also included an option for frequency hopping spread spectrum (FHSS), but that has largely been abandoned.

Adaptive ModulationWiFi make use of adaptive modulation and varying levels of forward error correction to optimize transmission rate and error performance.As a radio signal loses power or encounters interference, the error rate will increase.

Adaptive modulation means that the transmitter will automatically shift to a more robust, though less efficient, modulation technique in those adverse performance.

IEEE 802.11 modulations

OFDM

OFDM

OFDM transmitter

OFDM receiver

IEEE 802.11/xxx

OFDM Channels

3 steps for “live” signal acquisition

Bluetooth general features

Unlicensed 2.4GHz radio band• ISM (industrial, scientific,medical) band• Also used by Microwave ovens, 802.11, HomeRF…• Fast frequency hopping• 1600 (or 3200) hops/s• 79 frequencies• 1 MHz spacing• 220 μs switching time

Basic 10m range (with 0 dBm radio)• Extended 100m range (20 dBm)• Power classes• Class 1• Maximum output power: 100 mW (20 dBm)• Minimum output power: 1 mW (0 dBm)• Class 2• Maximum output power: 2.5 mW (4 dBm)• Minimum output power: 0.25 mW (-6 dBm)• Class 3• Maximum output power: 1 mW (0 dBm)

Bluetooth general features

Bluetooth is the name given to a new technology using short-range radio links, intended to replace the cable(s) connecting portable and/or fixed electronic devices. It is envisaged that it will allow for the replacement of the many propriety cables that connect one device to another with one universal radio link.

Its key features are robustness, low complexity, low power and low cost. Designed to operate in noisy frequency environments, the Bluetooth radio uses a fast acknowledgement and frequency hopping scheme to make the link robust.

Bluetooth radio modules operate in the unlicensed ISM band at 2.4GHz, and avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet. Compared with other systems in the same frequency band, the Bluetooth radio hops faster and uses shorter packets. The following pages give more detail about different sections of the protocol, note this tutorial is completely up to date with the latest version of the bluetooth Specification (ver 1.1)

Bluetooth SpectrumThe Bluetooth radio accomplishes spectrum spreading by frequency hopping in 79 hops displaced by 1 MHz, starting at 2.402GHz and finishing at 2.480GHz. In a few countries (i.e France) this frequency band range is (temporarily) reduced, and a 23-hop system is used. In order to comply with out of band regulations in each country. In both systems a guard band is used at the lower and upper band edge

Power Classes: Each device is classified into 3 power classes, Power Class 1, 2 & 3.

Bluetooth power classes

Power Class 1: is designed for long range (~100m) devices, with a max output power of 20 dBm,Power Class 2: for ordinary range devices (~10m) devices, with a max output power of 4 dBm,Power Class 3: for short range devices (~10cm) devices, with a max output power of 0 dBm. The Bluetooth radio interface is based on a nominal antenna power of 0dBm. Each device can optionally vary its transmitted power.Equipment with power control capability optimizes the output power in a link with LMP commands (see Link Manager Protocol). It is done by measuring RSSI and report back if the power should be increased or decreased.

Bluetooth modulation

Modulation Characteristics: The Bluetooth radio module uses GFSK (Gaussian Frequency Shift Keying) where a binary one is represented by a positive frequency deviation and a binary zero by a negative frequency deviation.

BT is set to 0.5 and the modulation index must be between 0.28 and 0.35.

Spurious Emissions: The spurious emission, in-band and out-of-band, is measured with a frequency hopping transmitter hopping on a single frequency; this means that the synthesizer must change frequency between receive slot and transmit slot, but always returns to the same transmit frequency.Radio

Frequency Tolerance: The transmitted initial center frequency accuracy must be ±75 kHz from Fc. The initial frequency accuracy is defined as being the frequency accuracy before any information is transmitted. Note that the frequency drift requirement is not included in the ±75 kHz.

Bluetooth performanceSensitivity Level: The receiver must have a sensitivity level for which the bit error rate (BER) 0.1% is met. For Bluetooth this means an actual sensitivity level of -70dBm or better.Interference

Performance: The interference performance on Co-channel and adjacent 1 MHz and 2 MHz are measured with the wanted signal 10 dB over the reference sensitivity level. On all other frequencies the wanted signal shall be 3 dB over the reference sensitivity level.

Out-of-Band blocking: The Out of band blocking is measured with the wanted signal 3 dB over the reference sensitivity level. The interfering signal shall be a continuous wave signal. The BER shall be less than or equal to 0.1%.

Originally Gaussian frequency-shift keying (GFSK) modulation was the only modulation scheme available; subsequently, since the introduction of Bluetooth 2.0+EDR, π/4-DQPSK and 8DPSK modulation may also be used between compatible devices. Devices functioning with GFSK are said to be operating in basic rate (BR) mode where an instantaneous data rate of 1 Mbit/s is possible. The term Enhanced Data Rate (EDR) is used to describe π/4-DPSK and 8DPSK schemes, each giving 2 and 3 Mbit/s respectively.

Bluetooth performanceBluetooth is a packet-based protocol with a master-slave structure. One master may communicate with up to 7 slaves in a piconet; all devices share the master's clock. Packet exchange is based on the basic clock, defined by the master, which ticks at 312.5 µs intervals.

Two clock ticks make up a slot of 625 µs; two slots make up a slot pair of 1250 µs. In the simple case of single-slot packets the master transmits in even slots and receives in odd slots; the slave, conversely, receives in even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots long but in all cases the master transmit will begin in even slots and the slave transmit in odd slots.

Bluetooth performanceA master Bluetooth device can communicate with up to seven devices in a piconet. (An ad-hoc computer network using Bluetooth technology) The devices can switch roles, by agreement, and the slave can become the master at any time.At any given time, data can be transferred between the master and one other device (except for the little-used broadcast mode). The master chooses which slave device to address; typically, it switches rapidly from one device to another in a round-robin fashion.The Bluetooth Core Specification provides for the connection of two or more piconets to form a scatternet, in which certain devices serve as bridges, simultaneously playing the master role in one piconet and the slave role in another.

Many USB Bluetooth adapters or "dongles" are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth dongles, however, have limited capabilities, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth with a distance of 100 meters, but they do not offer as many services as modern adapters do.