Introduction about what needs concerned among

Wi-Fi and Bluetooth Certification

Wakeyou Wang

Phone: 021-61278448

Mail to: wakeyou.wang@intertek.com

1. Foreword• In this rapid developing communication times, wireless

communication technology gets more and more, wider and wider application for its low cost, fast construction period and convenient use. And going with the improvement in technology, wireless communication has gently achieved the transmission speed to compare beauty with traditional fixed communication.

• There are many techniques to actualize wireless linking. In different application regions, what technology they need have different complexity. For example, if we just want to perform a remote control for a lamp, a wireless command with power on/off code is enough.We needn’t consider about the transmitting speed even about dependability ---- if failure transfers, do it once again. In contrary with it, some domains, such as telegraphy and telemetry, need a complex construction system to deal with transmitting rate, frequency confliction, internet linking and etc. Bluetooth, Wi-Fi, Wi-Max, HomeRF, ZigBee are representatives for the latter (with complex protocol system).

• Among the present civil domain, Bluetooth and Wi-Fi take the main parts. Here we mainly discuss about them two.

2. Definition

• Wi-Fi (wireless fidelity) concept is based and followed from Hi-Fi (high fidelity) which describes the quality of output signal generated by musical hardware. To make well-ordered management, “Wi-Fi alliance” was founded and in charge of all 802.11 certification (802.11 a/b/g/n and other future 802.11 protocol). The certified product can be considered it has very good RF compatibility with other wireless device.

At the beginning, only IEEE 802.11b certified product is Wi-Fi. But going with the technical development, IEEE 802.11g was also included in the Wi-Fi category. As for IEEE 802.11a product, because of working in 5GHz band, “Wi-Fi alliance” offers a different certification procedure and calls it Wi-Fi5.

• Bluetooth technology was developed originally by Ericsson, to obtain a low-cost and low-consumption radio interface between mobile telephones and their accessories.

• After that, some other telecommunication companies, such as IBM, INTEL, Nokia and Toshiba, joined in and created “SIG (Special Lobby Special Interest Group)” to maintain and develop this technique. IEEE also standardized it as IEEE 802.15.1.

• At present, Wi-Fi is mainly used to set a wireless LAN, connecting mounts of PC terminals and accessing to fixed network. Nevertheless, Bluetooth is more frequently applied to set up a personal area network (for example, wireless connection among PC, keyboard, mouse, headphone and sound box).

• This difference, in one hand, roots from their transfer rate: Wi-Fi can reach maximum 54Mbps while Bluetooth just reaches 1~3Mbps; in the other hand, based on their different power-consumption level, Wi-Fi is more suitable for fixed location use while Bluetooth is more outstanding in mobile use.

3. What is spreading spectrum technique?

• To improve transfer rate, a simple way is to expand the occupied frequency band. How to do this? Wi-Fi and Bluetooth represent two significant expanding methods: DSSS and FHSS.

• DSSS (Direct Sequence Spread Spectrum) is using many chips (more than 10) to represent for a bit of digital signal (0/1). Each chip is a signal with defined length and polarity. Here is an example below: (a) is the useful signal; (b) is the chip sequence. Digital signal (1) corresponds 11 chips and signal (0) corresponds 13 chips. By this, the original signal with high power and narrow band can be modified to a low-power density and broadband one.

信号幅度

时间

(A)

(B)

信号幅度

• FHSS (Frequency Hopping Spread Spectrum), by transmitting data at different frequency in time domain, achieves wide frequency band. In essentially, it is a kind of TDMA technology. At a certain time, the system hops at one channel and transmit some part of data and then, hops to another channel transmitting data----the hop sequence continues until all data transmitting finishes. Here is a pattern of 7 hops.

时间

频率频道1 频道2 频道3 频道4 频道5 频道6 频道7

1

2

3

4

5

6

7

功率密度

频率原始信号带宽

4. Modulation

• After spreading spectrum, we should modulate the signal so as to be fit for wireless transmitting.

• In 802.11b, there are three modulation method used: BPSK (binary phase shift keying), QPSK (quadraturephase shift keying) and CKK (complementary code keying, sometimes also called as CCK).

• The carrier of BPSK is transmitted to indicate a bit of digital signal (1) and the phase is reversed (shifted through 180°) to a bit of digital signal (0). Note that the phase shift does not have to be 180°, but this allows for the maximum separation of the digital states between 1 and 0, which is important when noise is prevalent. Here is an example while original phase 0° indicates digital signal (1):

As for QPSK, simply say, it is a system consisting of doubleBPSK. We call the two carriers of the double BPSK to be “I-carrier” and “Q-carrier”. The two carriers keep 90° angle difference and are sent to a summator. For that “I-carrier” and its reversed angle can indicate “0 and 1” while “I-carrier”and its reversed angle can indicate another group of “0 and 1”, each output signal from the summator stands for a two-bit code (00, 01, 10 or 11). As a result, the compositiveshifted phases are 45°, 135°, 225° and 315°. Here is sketch map below.

• In 802.11a, OFDM (orthogonal frequency division multiplexing) technology is used. OFDM is a multicarrier system. It divides the available spectrum into many narrow bands. Then the data is divided into parallel data streams and transmitted in parallel on these bands. Each band has a carrier and carrying data by varying its phase (general using QPSK).

• 802.11g also uses OFDM technology but simultaneity employing the same modulation method as 802.11b. This makes it be compatible with 802.11b and get a higher transmitting rate.

• Bluetooth: it divides the 2.4GHz ISM band up to 79 channels (USA and EU) that each occupies 1MHz. According to difference of modulation method, the system can reach transmission rate of 1Mbps (GFSK), 2Mbps (π/4-DQPSK) and 3Mbps (8DPSK).

6. Which standard should be applied for test?

• For CE verification, radio spectrum and electromagnetic compatibility characters are evaluated in different standards. For Bluetooth and Wi-Fi, their EMC part is assessed with EN301 489-1 & EN301 489-17. For radio spectrum part, The Bluetooth and 802.11b/g should be assessed with EN300 328 while 802.11a applied with EN301 893.

• For FCC certification, the assessment requirements about Bluetooth and Wi-Fi device are listed in two clauses --- FCC 47CFR part 15.247or 15.249. Compared with 15.247, part 15.249 has a stricter intentional emission limit and less number of test items. But if the intentional emission exceeds the limit, we have to choose 15.247 for test and bear amounts of test items (a list would be offered later).

• For IC certification, generally say, for Bluetooth and Wi-Fi, IC certification have same test requirement as FCC. So if FCC and IC certifications are applied at the same time, we can combine them in one test report. The applied standard is RSS 210.

• For C-tick certification. According to the risk of interference that may be expected from observed device, ACMA (Australian Communications and Media Authority) sorts radio-communication devices to three levels. The Bluetooth and Wi-Fi device are defined as level 2. That means, if a device has been certified by CE/FCC/IC, the corresponding report can be seen as the confidence of its satisfying with the mandated standards--- AS/ NZS 4771, without additional test needed.

7. Test condition

• In FCC part 15, measurements of the variation of fundamental frequency component of the emission, shall be performed with the supply voltage varied between 85% and 115% of the nominal rated supply voltage. For battery operated equipment, the equipment tests shall be performed using a new battery.

• In EN300 328, some test items need to be performed under normal condition as well as extreme condition. Here, “condition” includes two parts: working voltage and temperature. The normal temperature is +15 to +35 ; the normal voltage is the nominal mains voltage and frequency of AC mains shall be between 49 Hz and 51 Hz.

Generally, The extreme temperature is a range of -20~ +55. We always choose the two edge values as the representative. For working voltage, the extreme value is not same and decided by the type of power source used: AC mains, lead-acid battery, lithium or other battery. Take AC mains for instance: the extreme value is 0.9*normal voltage and 1.1*normal voltage. While testing, we set the extreme condition by combining the voltage and temperature. Among this standard, the tests that need to be conducted under extreme condition are “frequency range” and “e.i.r.p.”.

• In EN301 893, the extreme value of voltage and temperature is chosen from the user manual offered by the manufactory. Among this standard, the tests that also need to be conducted under normal condition as well as extreme condition are “carrier frequency” and “RF output power”.

• In EN301 489-1/-17, the test condition is similar as EN61000-6-1 & EN61000-6-3. Here we don’t offer a detailed introduction.

8. Test items• No matter for FCC or CE certification, if the Bluetooth or

Wi-Fi device has more than 3 channels, we need observe all the parameters in three channels: first, middle and last one except with special indication.

• Among FCC part 15.249, there are three test items in all. Here is the list below:1. Field Strength of Fundamental emission. This item restricts the strength of intentional RF signal. For common equipment, the limit is 94dBuV/m (50mV/m). This is rather low value so that it can be believed that the interference of fundamental emission to other device is very dim and additional evaluation is not necessary. Surely, we must ensure all the fundamental is among the allowed band. (2.4GHz or 5GHz ISM band), or the overflow part should be looked as spurious and assessed with items below.

• 2. Field Strength of harmonic emission. This item assesses the emission from harmonic points of fundamental.

• 3. Field Strength of emission not included above (neither fundamental nor harmonic).

• The standard lists three items above, nevertheless, for the Bluetooth and Wi-Fi device, no matter harmonics or general spurious, they have same limit: 54dBuV/m (500uV/m).

• Naturally, we need point that, the limit of fundamental (or e.i.r.p) and spurious emission mentioned in FCC standard, are the AV value. We also need to observe the PK reading with limit = AV limit + 20dB.

• Among FCC part 15.247, there are eleven test items in all. Some are offered especially for Bluetooth and some only for Wi-Fi. Here is the list below:

• 1. The maximum peak conducted output power. This item is to assess the fundamental emission. But here only conducted method is allowed, namely the test is conducted with a spectrum analyzer just at the RF output terminal with the antenna removed. We use PK detector and observe the total power within the occupied band of a channel (99% emission band).

• 2. Emission outside the frequency band. It can be performed either conducted or radiated method. The aim is to make sure the emission just outside the permitted band is low enough not influencing the outside band use. The detailed requirement is: maximum reading outside permitted frequency band should be at least 20dB less than the PK reading of fundamental emission.

3. Spurious emission. All emission outside permitted band is seen as spurious emission. As general requirement of Part 15, the tested range of spurious is 30MHz ~ at least 10th harmonic of fundamental.

4. Restrict band radiated emission. Especially for channels near the edge of permitted frequency band, some parts of the fundamental emission maybe drop in adjacent forbidden band. We need to observe this part and assess it with limit of spurious emission.

5. Power line conducted emission. This test is in all respects same as that in CISPR22. Here we don’t supply more introductions.

6. SAR. SAR is a parameter assessing the interference from emission of device to human body’s health.

7. Channel separation. This is a parameter especially for Bluetooth. It ensures the separation between two channels is high enough not happening interference with each other.

8. Channel number of hopping system, --- a parameter especially for Bluetooth. It relates the limit of “maximum peak conducted output power”. So we need to observe it first. Naturally, the device should work normally as actual use.

9. Average time of occupancy in one channel, --- a parameter also only for Bluetooth. As a hopping system, the device must satisfy the hopping rule: dwell time in any channel cannot be too long. Here is the detailed requirement: among the period of Numbers of channels*0.4 second, occupancy time on the observed channel shall not be greater than 0.4 second.

10. 6dB Bandwidth, --- a parameter especially for Wi-Fi to ensure this device is really a broadband one. From the highest reading, attenuated by 6dB, reading of this frequency range is looked as 6dB Bandwidth .It should be no less than 500 kHz.

11. Power spectrum density, --- a parameter also only for Wi-Fi, should be greater than 8dBm in any 3 kHz band. We just need to adjust the RBW= VBW = 3kHz, the maximum spectrum envelope reading is what we need test.

• Except those, the standard also restricts some parameters that set by the manufactory but should be confirmed by the certification engineer and described in report:

1. Type of antenna; generally FCC only allows the fix antenna or a removable one with a non-standard connector attached, so that the terminal user cannot replace it with a different antenna.

2. Gain of antenna. This parameter is used to combine with “maximum peak conducted output power” item to ensure the total radiated power is under a acceptable level. If the gain of antenna is too high, we should reduce the power supplied from RF output terminal to antenna.

• Among EN300 328, there is seven test items in all. Some are offered especially for Bluetooth and some only for Wi-Fi. Here is the list below:

• 1. Duty cycle. This is not a defined test item in this standard. But it participates in the calculation of “e.i.r.p.”and “e.i.r.p spectral density”, as a result, observation is necessary. We can test duty cycle as below: adjust the central frequency of spectrum analyzer to a nominal channel frequency, then set the span to zero. The observed “on / (on+off)” value is just what we want.

• 2. Maximum transmits power. This item is to assess the fundamental emission. It can be assessed with either conducted or radiated method. After that, we also need farther calculation together with duty cycle.

• 3. Frequency range. This parameter is to make sure the fundamental is among the permitted frequency band. And the observation is not based on power, but on power spectral density---the spectral density higher than -30dBm/100kHz should completely stay on permitted frequency band.

• 4. Transmitter spurious emission---This item is to observe the emission outside permitted frequency band both for stand-by and for transmit mode of transmitter. This test can be assessed with either conducted or radiated method.

• 5. Receiver spurious emission. This item is to observe the emission at any frequency when the equipment is in received mode.

• 6. Hopping requirements (channel number, channel separation and dwell time). This is an item only for Bluetooth device. The detailed introductions have been talked about in Part15.247 above. Here we don’t supply more introductions.

• 7. Max. e.i.r.p. spectral density --- an item only for Wi-Fi device, should be detected with AV detector while RBW = VBW = 1MHz. The power envelope showed is just “e.i.r.p. spectral density”. The maximum reading among the envelope should less than the limit: 10mW/MHz.

• Except those, the standard also restricts some parameters that set by the manufactory but should be confirmed by the certification engineer and described in report:

• 1. Medium access protocol --- is designed to facilitate spectrum sharing with other devices in a wireless network. The typical access protocol is the CSMA/CA (carrier sense multiple access with collision avoidance) mechanism. CSMA protocols are well known and also applied in Ethernet. But Ethernet uses the protocol based on CSMA/CD mechanism (CD for collision detection). “Collision detection” cannot be used in wireless network, because we cannot be sure that all the stations hear each other (which is the basic assumption of the collision detection principle). Moreover, ever if the transmitter checks the medium is free, it does not necessarily mean that the medium is also free for the receiver (for example, the receiver is a multipath channels).

• 2. Hopping sequence. This a parameter set for Bluetooth only to ensure the high- efficiency band use.

• Among EN301 893, here is seven test items in all. Here is the list below:

1. Duty cycle. This is not a defined test item in this standard. But it participates in the calculation of “RF output power” and “power density”.

2. Channel bandwidth. This parameter is observed under spectral density envelope. The 6dBc point with 100kHz RBW is the tested bandwidth.

3. RF output power along with TPC (transmit power control) technique. TPC technique is to control the transmitter output power resulting in reduced interference to other systems. If TPC technique is applied, the RF power should be tested under both the lowest and the highest power level of the TPC range. And the standard also sets the corresponding limit for those two conditions.

4. Power density along with TPC. This item should be tested as RF output power.

• 5. Transmitter unwanted emission inside & outside the specified band. The standard restricts the inside band unwanted emission by offering a defined figure of spectral envelope --- the inside emission should be all under the envelope. This test can be assessed with either conducted or radiated method.

• 6. Receiver spurious emission. It is emission at any frequency when the device is in receiving mode.

• 7. DFS (Dynamic frequency selection). To avoid co-channel operation with other systems, notably the radar systems, the device should have the ability to detect out the radar signal and dynamically select another channel, namely DFS. Limit to the present instruments in our shanghai lab, the DFS test should be subcontract to other competent lab.

• Except those, the standard also restricts some parameters that set by the manufactory but should be confirmed by the certification engineer and described in report:

• 1. Medium access protocol. (Please refer to the same item introduced under EN300 328)

• 2. User access restriction. DFS controls (hardware or software) related to radar detection shall not be accessible to the user so that the DFS requirements can neither be disabled nor altered.

• EN301 489-1 is a common EMC technical requirement for all RF device. It cites out detailed test condition, test items and limit / assessing criteria. As for test items and limit / assessing criteria, it is close to the combination of latest EN61000-6-1 and EN61000-6-3 except adding “Transients and surges” item especially for vehicular device. Here we don’t offer detailed description.

• EN301 489-17 lists special technical requirement for Bluetooth and Wi-Fi. It should be used together with EN301 489-1. But if there’s any difference on a same object, EN301 489-17 takes precedence. Seen from the concrete content in EN301 489-17, we can find that it mainly focus on more detailed performance criteria.

9. Category of antenna and corresponding test method

• Among Part 15.249, all the tests should be performed with “radiated” method; Among Part 15.247, EN300 328 and EN301 893, the test method should be chosen based on the category of transmitting antenna.

• 1. For integral antenna (fixed antenna or antenna attached a non-standard connector), all tests should be performed with “radiated” method.

• 2. For removable antenna with a standard connector, except spurious emission which should be assessed with radiated method, all other tests can be performed with “conduct” method.

3. For multiple transmit chains (more than one transmit antenna and those antennae can work simultaneously), if “radiated” method chosen, all tests should be done with one antenna active while others are disable. If “conducted” method chosen, all the RF output ports should be combined with a power splitter / combiner while all the antennas are active.

• No matter in FCC or CE standard, the “conducted”method is similar: the assessed signal, from the RF output terminal of device, is transferred completely by conducted approach to terminal measurement instrument. The general approach frame is “RF port of device→assistant test equipment (for example, attenuator)→measurement instrument”.

• But the meaning of “radiated” method is different in FCC and CE standard, especially in “e.i.r.p.” and “spurious emission” test. In FCC standard, the parameters are assessed with “anechoic chamber(radiation of device→receiving antenna)→assistant test equipment→measurement instrument" system. The detected field strength is the last result and can be directly compared with limit. In CE standard, the detected field strength is just a midway assistant value. After the reading of field strength is achieved, we need remove the device under test out of the anechoic chamber, and replace with a substitution system (consists of a signal generator and a standard transmitting antenna) at where the device is originally put. At a certain frequency point we need to assess, the signal generator should be adjusted until the generated field strength is same as that of device under test. The output RF power of the substitution system is seen as the strength of device at the frequency point where the signal generator is set.

• Although the “radiated” and “conducted” method is paratactic, the “conducted” method has better precision and as a result can offer a better test identity. So if possible, we should choose “conducted” method as preferred option.

10. How to deliver application for certification?

• For CE verification: after the test report is finished, our shanghai lab can issue the verification directly without the need of reporting to any other organization or individual.

• For FCC certification: after the test report is finished, we must prepare some other papers, and together with test report, sent to a TCB lab (“telecommunication certification body” lab, which is accredited by FCC) for certification applying. Because our USA company ---“Intertek NA” is a such lab, we often apply certification via it.

• Well, before or among FCC certification, the applicant also needs to offer some help:

• 1. Offer samples to us as requirement as below:

Bluetooth device: ①. One sample equipped with an antenna for real sale and another attached with a SMA connector just at the RF output terminal (make sure the correct impedance matching); ②. The control program can be set to hop on a certain channel (at least first channel, middle channel and last channel) and hop as normal working; ③. DH1, DH5 (Packet Type) selection mode, if it would support DH5.

Wi-Fi device: ①. One sample equipped with an antenna for real sale and another attached with a SMA connector just at the RF output terminal (make sure the correct impedance matching); ②. The control program can be set to select a certain channel (at least first, middle and last channel) under continuous transmit & maximum transmitting rate mode.

SMA (Male) SMA (Female)

N (Male) N (Female)

• 2. The applicant should tell us the FCC ID of the device.

The FCC ID consists of two parts: “grantee code”

and “product code”.

“Grantee code” (consists of three alphanumeric characters (chosen from A-Z, 0-9)) is a degree code of the applicant and offered by FCC. Naturally, the conferring is not free: $60 each. The application for grantee code can be conveniently achieved in the FCC web: https://fjallfoss.fcc.gov/oetcf/eas/forms/GranteeRegistration.cfm.

The “product code” is the product degree code designed by the applicant. But there is a designing rule: at most 14 characters (chosen from “-”, A-Z, 0-9).

Note: similar as FCC ID, IC also consists of two parts:“company number” and “unique product number”.

“company number” (consists of six alphanumeric characters (chosen from A-Z, 0-9)) is a degree code of the applicant and offered by IC(industry Canada). The application is convenient by e-mailing to:

certification.bureau@ic.gc.ca with detailed applicant’s information. Generally, the reply is very soon and offers a company number without charge.

The IC format is ---- IC: XXXXXX-YYYYYYYYYYY. The “XXXXXX” is “company number”; “YY” is “unique product number” which consists at most 11 characters (chosen from A-Z, 0-9).

• 3. Block diagram (showing all internal oscillators and clock frequencies)

• 4. Schematic diagram of the RF part. (at least showing the most basic integrate circuit)

• 5. Document for antenna (type, gain, input impedance and pattern diagram etc.)

Generally, the 50Ω input impedance is used. If any deviation, please indicate.

• 6. Component list (BOM).

• 7. ID label (may include FCC ID, product name, model, ratings, brand or others, but only FCC ID is absolutely necessarily).

• 8. Technical Description of transmitter. You can give a RF module description or technical characters of the device itself.

• 9. User manual. 1) Warning: CHANGES OR MODIFICATIONS

NOT EXPRESSLY APPROVED BY THE PARTYRESPONSIBLE FOR COMPLIANCE WITH THEFCC’ RULES ( THE FCC’ GRANTEE’ ) COULD VOIDTHE USER’S AUER’S AUTHORITY TO OPERATETHE EQUIPMENT.

2)THIS DEVICE COMPLIES WITH PARTS 15 OF THEFCC RULES. OPERATION IS SUBJECT TO THEFOLLOWING TWO CONDITIONS: (1) THIS DEVICEMAY NOT CAUSE HARMFUL INTERFERENCE,AND (2) THIS DEVICE MUST ACCEPT ANYINTERFERENCE RECEIVED. INCLUDINGINTERFERENCE THAT MAY CAUSE UNDESIREDOPERATION.

• 3) Note: This equipment has been tested and found to comply withthe limits for a Class B digital devices, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses an can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interferencewill not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by tuning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

1. Reorient or relocate the receiving antenna.

2. Increase the separation between the equipment and receiver.

3. Connect the equipment into an outlet on a circuit different from

that to which the receiver is connected.

4. Consult the dealer or an experienced radio/TV technical for help.

4) Maximum Permissible Exposure reminding.

As a mobile device, we need give a reminding that,

“This product is a mobile device and the distance between that and the user or nearby persons should no less than 20cm under normal operational condition.”

Sometimes, because of too high RF power, after test, we found that the 20cm cannot keep the nearby person safety enough. We would offer a larger distance calculated with actual power.

• For IC certification: after the test report is finished, we must prepare the papers same as FCC application, and together with test report, sent to a CB (“certification body”which is recognized by “IC” to certify equipment in conformity to the Canadian radio communication / broadcasting requirements) for certification applying. Because our USA company --- “Intertek NA” is a such organization, we also apply certification via it.

Thanks!