24-06-2011, 10:19 AM
PRESENTED BY:
RITESH
[attachment=14305]
INTRODUCTION
Bluetooth technology has become indispensible on today’s mobile phones. Bluetooth and cellular technologies on the same device, referred to as the coexistence of two technologies, has become paramount as both technologies continue to evolve.
For example, is to use hands free Bluetooth headset while 4G radio receiving phone calls during driving.
4G technologies commonly include mobile Wi MAX (worldwide interoperability for microwave access ) and LTE(Long term evolution).
Only two significant allocations exist in United States- the wireless communication services(WCS) ,also known as Wibro in South korea , located at 2.3-2.4 GHz and multichannel multipoint distribution systems(MMDS) located in 2.5-2.7 GHz.
Globally, the 2500-2690 MHz band, specified as the”IMT-2000 expansion band” by the International Telecommunication Union(ITU) ,has been opened up for the potential deployment of Wi MAX and LTE systems.
Continued……
The figure 1 shown below gives the spectrum for Bluetooth and 4G wireless technologies.
We use analytical and real experiments results to show that dominant co-existence Bluetooth/4G usage cases with demand in real-time traffic can be well supported using simple and low cost Time-Domain co-existences.
BLUETOOTH
Bluetooth supports bit rate of 1Mbps at basic rate ,2 or 3 Mbps at enhanced data rate.
Connection is established between a master and a group of slave devices ; all devices are synchronized to a common clock and frequency.
A TDD scheme is used where master and slave alternately transmit.
Two types of connections are defined between master and a slave
Extended)Synchronous Connection-Oriented (SCO/eSCO)connection and Asynchronous Connection-Oriented(ACL)connection.
SCO/eSCO supports time-bounded information like voice , and is maintained by using reserved slots at regular time intervals.
In the slots not reserved for SCO/eSCO, the master may exchange packets with any slave to support asynchronous data transfer.
For most ACL packets , packet retransmission is applied to ensure data integrity.
4G TECHNOLOGY
Both WiMAX and LTE are telecommunications technologies that intend to provide broadband wireless service based on point-to-multipoint connections.
WiMAX and LTE both support frequency-division duplex(FDD) as well as time-division duplex(TDD) systems.
In TDD systems, uplink and downlink transmissions within a cell operate on the same frequency, with separation in time.
Each 4G radio frame in TDD mode is divided into two subframes : a downlink frame(transmission from BS to MS) followed by an uplink subframe (transmission from MS to BS) with small guard intervals in between.
INTERFERENCE ANALYSIS
There are two primary sources of radio to radio interference:
One is the transmitter out-of-band emission
The other is receiver blocking or saturation due to nonlinearity of RF receiving chain.
We examine each of them below
BLUETOOTH RECEIVER SATURATION
RF circuits can be approximated with linear models for small input signals, nonlinearities appear as signal amplitude increases.
Often the output of the circuit is a “compressive” or “saturating” function of the input. This effect is captured by “3 db compression point” –referring to the input signal amplitude at which the low noise amplifier(LNA) gain is reduced by 3db.
When LNA goes into compression, there is less gain available to amplify the small unwanted signals , thus the receiver’s sensitivity.
4G signals in 2.5-2.69 GHz or 2.3—2.4 GHz should be attenuated by 65 db before reaching Bluetooth LNA to avoid sensitivity loss caused by receiver saturation.
Continued………
B. INCREASE OF NOISE FLOOR
OOB emission from 4G radio is a wide band noise that falls within receiving band of Bluetooth radio and hence raises the noise floor of Bluetooth radio . This results in loss of sensitivity and operating range for Bluetooth.
Noise figure defined as NF=SNRin / SNRout is a measurement of how much the SNR degrades as the signal passes through the systems.
C. FILTERING AND ANTENNA ISOLATION REQUIREMENTS
The required interference signal attenuation from aforementioned analysis can be achieved through the combination of antenna and filtering.
While antenna isolation can vary with different antenna placements and orientations, the achievable antenna isolation is fundamentally limited by the size of the device.
BLUETOOTH COEXISTENCE WITH 4G TDD SYSTEMS
The focus of this part is on the coexistence of Bluetooth radio with 4G TDD systems . Our goal is to support sufficient Bluetooth performance under worst case 4G radio interference ,i.e. , the 4G radio transmits during the entire UL sub frame of each TDD frame.
CLOCK ALIGNMENT BETWEEN BLUETOOTH AND 4G RADIOS
The key solution to prevent from interference is to maximize the probability of Bluetooth receptions occurring during 4G DL duration.
4G radio frame is the unit of Bluetooth slot where frame is divided into DL/UL duration.
The figure shown below gives the relative timing between between Bluetooth and 4G radios.
Continued………
B. FEASABILITY OF CLOCK ALIGNMENT
Clock alignment between Bluetooth and 4G requires Bluetooth radio to adjust its slot boundary based on 4G radio frame timing .
The conceptual illustration for the signalling between co-located Bluetooth and 4G radios is shown below.
The alignment involves the slot boundary of Bluetooth piconet being shifted in time and amount of shifts in the range of[-625us,+625us] as shown.
Continued………….
The frequency hopping sequence of Bluetooth radio is not changed ,nor does its clock cycle duration.
BLUETOOTH PERFORMANCE UNDER ASYNCHRONOUS CONNECTIONS
Bluetooth audio uses asynchronous connection to transfer audio files from laptop/smart phone to stereo headset.
Bluetooth radio needs to transmit outgoing audio packets and receive incoming acknowledgement packet correctly.
Bluetooth link controller is responsible for deciding which and when packet size to transmit under constraints.
A. Co-located Bluetooth Radio as Master
A continuous stream of 5-slot packet transmission is considered when co-located Bluetooth radio is master. Each 5-slot TX followed by 1-slot acknowledgement RX and successive transmissions are 6 slot apart.
The requirement for correct Bluetooth reception can be represented as
TXoffset+5+6m=d+8n
Where d represents 4G DL duration .The left hand side of the above equation represents the RX slot while the right hand side represents
the repetitive DL duration of 4G radio frames.
Continued………………
B.C0-located Bluetooth Radio as Slave
Slave can only transmit after it receives from the master first and the transmission is successful only if the slave receives the immediate acknowledgement from the master . In other words, two successive receptions are required for one successful transmission.
C. Traffic Demand of A2DP Audio Streaming
A2DP source device determines A2DP packet inter-arrival period based on the maximum transmission unit(MTU) size at the receiving device.
Each A2DP packet is fragmented to multiple ACL packets at base band controller, which determines which packet size and which modulation to use.
BLUETOOTH PERFORMANCE UNDER SYNCHRONOUS CONDITIONS
Bluetooth Extended Synchronous Connection Oriented (eSCO) link is intended to carry constant data traffic such as voice.
eSCO connection can be set up to provide limited retransmissions for lost or damaged packets inside a retransmission windows.
The number of retransmissions required for eSCO packets due to 4G radio interference is minimized if Bluetooth pico net clock is properly aligned with 4G radio frame timing . consequently, the retransmission oppurtunities left to combat packet losses resulting from poor channel condition is maximized for coexistence usage cases.
EXPERIMENTAL RESULTS
A. Test Setup
The above figure shows the logical setup to measure the Bluetooth application performance under 4G radio interference environment.
A 4G connection and Bluetooth connection is established through cables.L1,L2 and L3 each represents a set of attenuators that control the attenuation in 4G link, Bluetooth link and antenna isolation.
Continued……….
Value of L3 characterizes the additional antenna isolation.L1,L2 and L3 can be directly translated to distances between devices given the path loss mode.
Oscilloscope , network analyzer, signal generator and logical analyzer are also integrated into the configuration to probe the real-time behavior.
B. Bluetooth Radio Interfered By Co-located 4G Radio
To demonstrate that 4G radio causes significant interference to the co-located Bluetooth radio , we use Bluetooth SCO connection (commonly known as HV3) to transmit a voice clip from remote Bluetooth device , where the co-located Bluetooth radio serves as master.
There is no retransmission for SCO connection , hence every Bluetooth reception interfered by Wi MAX transmission leads to a packet loss. The co-located Wi MAX radio is configured to transmit during each frame for the entire UL sub frame duration.
Continued…………………
We used PESQ(Perceptual Evaluation of Speech Quality) tool from Optimum (Q-Master Voice Analyzer) to evaluate the receiving voice quality at co-located Bluetooth radio.
The figure shown below gives the Bluetooth voice quality over SCO (HV3) interfered by 4G radio.
Continued……………..
C. Bluetooth Voice Quality Improvements
With limited eSCO retransmission capability and clock alignment between co-located Bluetooth radios , Bluetooth voice quality can be preserved even under the worst case 4G interference.
The figure shown below Bluetooth voice quality with eSCO and clock alignment.
Continued…………………
D. Audio Streaming Quality Experiments
Co-located Bluetooth radio transfers audio file to an sink ,where the received audio is saved into a wave file for audio quality benchmark . It is done using PEAQ(Perceptual Evaluation of Audio Quality) algorithm from Opticom (OPERA software suite).
The figure shown below gives audio streaming experiments result for packet loss ratio, maximum jitter , PEAQ score.
Continued………………..
CONCLUSION
It is critical to support the coexistence of Bluetooth and 4G radios to enable popular usage cases that require simultaneous operations of both radios.
Simple time domain coexistence solutions can maximize Bluetooth performance and support dominant coexistence usage cases with real time traffic under worst case 4G interference.
The proposed solution provides an effective and low cost approach to solve Bluetooth/4G coexistence issues ,with minimal impact on Bluetooth radio and no impact on 4G device/network deployment
RITESH
[attachment=14305]
INTRODUCTION
Bluetooth technology has become indispensible on today’s mobile phones. Bluetooth and cellular technologies on the same device, referred to as the coexistence of two technologies, has become paramount as both technologies continue to evolve.
For example, is to use hands free Bluetooth headset while 4G radio receiving phone calls during driving.
4G technologies commonly include mobile Wi MAX (worldwide interoperability for microwave access ) and LTE(Long term evolution).
Only two significant allocations exist in United States- the wireless communication services(WCS) ,also known as Wibro in South korea , located at 2.3-2.4 GHz and multichannel multipoint distribution systems(MMDS) located in 2.5-2.7 GHz.
Globally, the 2500-2690 MHz band, specified as the”IMT-2000 expansion band” by the International Telecommunication Union(ITU) ,has been opened up for the potential deployment of Wi MAX and LTE systems.
Continued……
The figure 1 shown below gives the spectrum for Bluetooth and 4G wireless technologies.
We use analytical and real experiments results to show that dominant co-existence Bluetooth/4G usage cases with demand in real-time traffic can be well supported using simple and low cost Time-Domain co-existences.
BLUETOOTH
Bluetooth supports bit rate of 1Mbps at basic rate ,2 or 3 Mbps at enhanced data rate.
Connection is established between a master and a group of slave devices ; all devices are synchronized to a common clock and frequency.
A TDD scheme is used where master and slave alternately transmit.
Two types of connections are defined between master and a slave
Extended)Synchronous Connection-Oriented (SCO/eSCO)connection and Asynchronous Connection-Oriented(ACL)connection.SCO/eSCO supports time-bounded information like voice , and is maintained by using reserved slots at regular time intervals.
In the slots not reserved for SCO/eSCO, the master may exchange packets with any slave to support asynchronous data transfer.
For most ACL packets , packet retransmission is applied to ensure data integrity.
4G TECHNOLOGY
Both WiMAX and LTE are telecommunications technologies that intend to provide broadband wireless service based on point-to-multipoint connections.
WiMAX and LTE both support frequency-division duplex(FDD) as well as time-division duplex(TDD) systems.
In TDD systems, uplink and downlink transmissions within a cell operate on the same frequency, with separation in time.
Each 4G radio frame in TDD mode is divided into two subframes : a downlink frame(transmission from BS to MS) followed by an uplink subframe (transmission from MS to BS) with small guard intervals in between.
INTERFERENCE ANALYSIS
There are two primary sources of radio to radio interference:
One is the transmitter out-of-band emission
The other is receiver blocking or saturation due to nonlinearity of RF receiving chain.
We examine each of them below
BLUETOOTH RECEIVER SATURATION
RF circuits can be approximated with linear models for small input signals, nonlinearities appear as signal amplitude increases.
Often the output of the circuit is a “compressive” or “saturating” function of the input. This effect is captured by “3 db compression point” –referring to the input signal amplitude at which the low noise amplifier(LNA) gain is reduced by 3db.
When LNA goes into compression, there is less gain available to amplify the small unwanted signals , thus the receiver’s sensitivity.
4G signals in 2.5-2.69 GHz or 2.3—2.4 GHz should be attenuated by 65 db before reaching Bluetooth LNA to avoid sensitivity loss caused by receiver saturation.
Continued………
B. INCREASE OF NOISE FLOOR
OOB emission from 4G radio is a wide band noise that falls within receiving band of Bluetooth radio and hence raises the noise floor of Bluetooth radio . This results in loss of sensitivity and operating range for Bluetooth.
Noise figure defined as NF=SNRin / SNRout is a measurement of how much the SNR degrades as the signal passes through the systems.
C. FILTERING AND ANTENNA ISOLATION REQUIREMENTS
The required interference signal attenuation from aforementioned analysis can be achieved through the combination of antenna and filtering.
While antenna isolation can vary with different antenna placements and orientations, the achievable antenna isolation is fundamentally limited by the size of the device.
BLUETOOTH COEXISTENCE WITH 4G TDD SYSTEMS
The focus of this part is on the coexistence of Bluetooth radio with 4G TDD systems . Our goal is to support sufficient Bluetooth performance under worst case 4G radio interference ,i.e. , the 4G radio transmits during the entire UL sub frame of each TDD frame.
CLOCK ALIGNMENT BETWEEN BLUETOOTH AND 4G RADIOS
The key solution to prevent from interference is to maximize the probability of Bluetooth receptions occurring during 4G DL duration.
4G radio frame is the unit of Bluetooth slot where frame is divided into DL/UL duration.
The figure shown below gives the relative timing between between Bluetooth and 4G radios.
Continued………
B. FEASABILITY OF CLOCK ALIGNMENT
Clock alignment between Bluetooth and 4G requires Bluetooth radio to adjust its slot boundary based on 4G radio frame timing .
The conceptual illustration for the signalling between co-located Bluetooth and 4G radios is shown below.
The alignment involves the slot boundary of Bluetooth piconet being shifted in time and amount of shifts in the range of[-625us,+625us] as shown.
Continued………….
The frequency hopping sequence of Bluetooth radio is not changed ,nor does its clock cycle duration.
BLUETOOTH PERFORMANCE UNDER ASYNCHRONOUS CONNECTIONS
Bluetooth audio uses asynchronous connection to transfer audio files from laptop/smart phone to stereo headset.
Bluetooth radio needs to transmit outgoing audio packets and receive incoming acknowledgement packet correctly.
Bluetooth link controller is responsible for deciding which and when packet size to transmit under constraints.
A. Co-located Bluetooth Radio as Master
A continuous stream of 5-slot packet transmission is considered when co-located Bluetooth radio is master. Each 5-slot TX followed by 1-slot acknowledgement RX and successive transmissions are 6 slot apart.
The requirement for correct Bluetooth reception can be represented as
TXoffset+5+6m=d+8n
Where d represents 4G DL duration .The left hand side of the above equation represents the RX slot while the right hand side represents
the repetitive DL duration of 4G radio frames.
Continued………………
B.C0-located Bluetooth Radio as Slave
Slave can only transmit after it receives from the master first and the transmission is successful only if the slave receives the immediate acknowledgement from the master . In other words, two successive receptions are required for one successful transmission.
C. Traffic Demand of A2DP Audio Streaming
A2DP source device determines A2DP packet inter-arrival period based on the maximum transmission unit(MTU) size at the receiving device.
Each A2DP packet is fragmented to multiple ACL packets at base band controller, which determines which packet size and which modulation to use.
BLUETOOTH PERFORMANCE UNDER SYNCHRONOUS CONDITIONS
Bluetooth Extended Synchronous Connection Oriented (eSCO) link is intended to carry constant data traffic such as voice.
eSCO connection can be set up to provide limited retransmissions for lost or damaged packets inside a retransmission windows.
The number of retransmissions required for eSCO packets due to 4G radio interference is minimized if Bluetooth pico net clock is properly aligned with 4G radio frame timing . consequently, the retransmission oppurtunities left to combat packet losses resulting from poor channel condition is maximized for coexistence usage cases.
EXPERIMENTAL RESULTS
A. Test Setup
The above figure shows the logical setup to measure the Bluetooth application performance under 4G radio interference environment.
A 4G connection and Bluetooth connection is established through cables.L1,L2 and L3 each represents a set of attenuators that control the attenuation in 4G link, Bluetooth link and antenna isolation.
Continued……….
Value of L3 characterizes the additional antenna isolation.L1,L2 and L3 can be directly translated to distances between devices given the path loss mode.
Oscilloscope , network analyzer, signal generator and logical analyzer are also integrated into the configuration to probe the real-time behavior.
B. Bluetooth Radio Interfered By Co-located 4G Radio
To demonstrate that 4G radio causes significant interference to the co-located Bluetooth radio , we use Bluetooth SCO connection (commonly known as HV3) to transmit a voice clip from remote Bluetooth device , where the co-located Bluetooth radio serves as master.
There is no retransmission for SCO connection , hence every Bluetooth reception interfered by Wi MAX transmission leads to a packet loss. The co-located Wi MAX radio is configured to transmit during each frame for the entire UL sub frame duration.
Continued…………………
We used PESQ(Perceptual Evaluation of Speech Quality) tool from Optimum (Q-Master Voice Analyzer) to evaluate the receiving voice quality at co-located Bluetooth radio.
The figure shown below gives the Bluetooth voice quality over SCO (HV3) interfered by 4G radio.
Continued……………..
C. Bluetooth Voice Quality Improvements
With limited eSCO retransmission capability and clock alignment between co-located Bluetooth radios , Bluetooth voice quality can be preserved even under the worst case 4G interference.
The figure shown below Bluetooth voice quality with eSCO and clock alignment.
Continued…………………
D. Audio Streaming Quality Experiments
Co-located Bluetooth radio transfers audio file to an sink ,where the received audio is saved into a wave file for audio quality benchmark . It is done using PEAQ(Perceptual Evaluation of Audio Quality) algorithm from Opticom (OPERA software suite).
The figure shown below gives audio streaming experiments result for packet loss ratio, maximum jitter , PEAQ score.
Continued………………..
CONCLUSION
It is critical to support the coexistence of Bluetooth and 4G radios to enable popular usage cases that require simultaneous operations of both radios.
Simple time domain coexistence solutions can maximize Bluetooth performance and support dominant coexistence usage cases with real time traffic under worst case 4G interference.
The proposed solution provides an effective and low cost approach to solve Bluetooth/4G coexistence issues ,with minimal impact on Bluetooth radio and no impact on 4G device/network deployment