TECHNICAL FIELD

Embodiments herein relate to an integrated wireless communication and radar system. In particular, they are an integrated wireless communication and radar system for operating radar and communication mode simultaneously.

BACKGROUND

A wireless communication transceiver and a radar sensor may be integrated. Such kind systems are applicable in vehicle-to-vehicle communication and distance/speed measurements, as well as in unmanned aerial vehicles-to-vehicle, e.g. drone

communication and distance/speed measurements. A group of drones can work together to collect information and to monitor a certain area. The communication and distance measurement become important. Furthermore, due to limited weight and space for a drone, margining radar and communication system is desired.

A group of sensors, for instance to monitor temperature/smoke/moisture, etc. in an open field, need a communication network and a positioning network, the distance measurement system between sensors can provide a position or a relative position information, to replace Global Positioning System (GPS) or act as a backup GPS.

In health-care and wearable health-care system for obtaining and transmitting vital signs from sensors to repositories or other units. Several approaches have been applied to realize the dual functions system.

In CN 105182323, a ZigBee communication module are added in a radar system. So the communication system and radar system are independent. The chip area and DC power consumption are probably larger than other integrated solutions.

In G.N. Saddik, R.S. Singh, E.R. Brown, " Ultra-wideband multifunctional communications/radar system", IEEE Trans. Microw. Theory Tech., 2007, 55, (7), pp. 1431-1437, a pulse radar signal and a pulse communication signal are transmitted and received in the same platform. To compress the pulses, a up-chirp and a down-chirp linear frequency modulation are used for the radar signal and the communication signal, respectively. Furthermore, the transmitted waves, i.e. the radar and communication signals, are right-hand circularly polarised (RHCP). The communication receiver receives only RHCP signal, and the radar receiver receives only left-hand circularly polarised (LHCP) signal since the reflection of the radar signal changes the rotation direction. The isolation of the different polarizations is utilized to separate the radar and communication signal at the receivers. However, the pulse radar is often expensive in manufacture and maintenance, comparing with a frequency modulated continuous wave (FMCW) radar.

Time-domain duplex is also used in prior art for integrating radar and wireless communication transceiver. These systems work alternately in the radar mode and communication mode. In the communication mode, different kinds of modulation are applicable, for instance, a BPSK and QPSK modulations, an ultra-wide band (UWB) frequency modulation, a FSK modulation etc. In the radar mode, different kinds of frequency modulations are utilized for radar waves too. For example, a continuous linear frequency modulate radar wave, a stepped frequency modulated radar wave etc.. In a so- called FSK radar, transmitter sends out two frequencies signals in an intertwined sequence. However, in these solutions, it does not allow the radar and communication operating simultaneously. Thus, the capability of the communication is reduced, and the radar measurement is discontinuous.

SUMMARY

Therefor it is an object of embodiments herein to provide an integrated wireless communication and radar system with improved performance.

According to a first aspect of embodiments herein, the object is achieved by an integrated wireless communication and radar system for operating radar and

communication mode simultaneously. The system comprises a transmitter configured to transmit a chirped FSK modulated signal for both communication and radar

measurement, where communication data, represented by a binary sequence, and a chirp radar signal, e.g. a frequency modulated sawtooth wave signal, are combined to form the chirped FSK modulated signal. The transmitter comprises an encoder for encoding the communication data such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data.

The system further comprises a receiver configured to receive a first chirped FSK modulated signal reflected from a reflector and a second chirped FSK modulated signal transmitted from other wireless communication and radar system.

The receiver comprises a communication receiver and a radar receiver. The radar receiver is configured to filter-out the communication signal in the first chirped FSK modulated signal to obtain a radar signal for distance and/or speed measurement. The communication receiver is configured to demodulate the second chirped FSK modulated signal and obtain the communication data.

According to a second aspect of embodiments herein, the object is also achieved by a transmitter for operating radar and communication mode simultaneously. The transmitter comprises an encoder for encoding communication data represented by a binary sequence such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data. The transmitter is configured to combine the encoded communication data and a chirp radar signal to form a chirped FSK modulated signal and transmit the chirped FSK modulated signal for both communication and radar measurement. According to a third aspect of embodiments herein, the object is achieved by a method performed in an integrated wireless communication and radar system for operating radar and communication mode simultaneously. The integrated wireless communication and radar system encodes communication data represented by a binary sequence such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data. The integrated wireless communication and radar system generates a chirped FSK modulated signal from the encoded

communication data and a chirp radar signal. Then the integrated wireless

communication and radar system transmits the chirped FSK modulated signal for both communication and radar measurement.

In another words, according to the embodiments herein, a wireless communication using chirped FSK modulation and a FMCW radar system are integrated in a single system. A chirped FSK modulated signal is used for both communication and radar measurement, where communication data, represented by a binary sequence, and a chirp radar signal are combined to form the chirped FSK modulated signal. The chirped FSK signal may be generated by a single sideband mixer. The encoder, e.g. a so-called 8-bit to 10-bit encoder, encodes the communication data such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data.

Consequently, the FSK signal may be removed in the radar receiver by averaging the FSK pulse's frequencies in time domain. In the communication receiver, the chirped FSK signal may be demodulated by mixing the received chirped FSK signal send by other integrated wireless communication and radar system with a sawtooth wave synchronized to the received signal, and then using a conventional FSK demodulator. The

communication data may be then obtained after decoding, e.g. an 8-bit to 10-bit decoding.

In this way, the wireless communication and radar sensor may work simultaneously, thus, the communication capability, e.g. data rate, is improved, comparing with the time- domain duplex solution. While, the distance/speed measurements can be carried out continuously. In the radar receiver, the wireless communication signal is removed in digital domain with a simple average algorithm. This solution is much simpler than the transceiver with circularly polarized microwave. Furthermore, both wireless

communication transceiver and radar sensor operate in the same frequency band, so they may share the same packaging, antennas, as well as a part of microwave circuits, e.g., a power amplifier, a low noise amplifier etc.. Thus, embodiments herein provide an improved communication and radar system which can operate in radar and communication mode simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 is a general view of an integrated wireless communication and radar system according to the embodiments herein;

Figure 2 is a block diagram of a transmitter according to embodiments herein;

Figure 3 is a diagram illustrating a frequency modulated sawtooth signal in time-domain; Figure 4 is a diagram illustrating a chirped FSK modulated signal (not to scale);

Figure 5 is a block diagram of a radar receiver according to embodiments herein;

Figure 6 is a diagram illustrating a reflected wave and a frequency modulated sawtooth wave at the radar receiver (not to scale);

Figure 7 is a block diagram of an image reject mixer (IRM) according to embodiments herein;

Figure 8 are diagrams showing (a) a sawtooth wave and a reflected wave; (b) lower sideband output of the IRM in Figure 7 (not to scale); Figure 9 are diagrams showing (a) a sawtooth wave and a reflected wave; (b) lower sideband output, and (c) up sideband output of the I RM in Figure 7 (not to scale);

Figure 10 are diagrams showing a reflected radar signal, received communication signal, and a synchronized sawtooth wave in time-domain (not to scale) with different delay times Tdo to the input sawtooth wave (a) Tdo=0 and (b)Tdo≠0; Figure 1 1 is a block diagram of a communication receiver according to embodiments herein;

Figure 12 is a block diagram of a FSK demodulator;

Figure 13 is a flow chart illustrating a method performed in an integrated wireless

communication and radar system according to embodiments herein; Figure 14 is a block diagram illustrating an electronic device in which embodiments herein may be implemented. DETAILED DESCRIPTION

An integrated wireless communication and radar system 100, i.e. a chirped FSK wireless transceiver and a FMCW radar sensor are integrated in a single system, for operating radar and communication mode simultaneously, is shown in Figure 1.

The integrated wireless communication and radar system 100 comprises a transmitter 110 configured to transmit a chirped FSK modulated signal 120 for both communication and radar measurement. Communication data, represented by a binary sequence, and a chirp radar signal are combined to form the chirped FSK modulated signal 120.

The communication/radar signal transmitter 1 10 comprises an encoder 112 for encoding the communication data such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data.

The system 100 further comprises a receiver 130 configured to receive a first chirped FSK modulated signal reflected from a reflector and a second chirped FSK modulated signal transmitted from other wireless communication and radar system.

The receiver 130 comprises a radar receiver 131 and a communication receiver

132.

The radar receiver 131 is configured to filter-out the communication signal in the first chirped FSK modulated signal to obtain a radar signal for distance and/or speed measurement. The communication receiver 132 is configured to demodulate the second chirped FSK modulated signal and obtain the communication data. To decode the encoded communication data, the communication receiver 132 may further comprises a decoder 133 corresponding to the encoder 1 12 in the transmitter 1 10.

The inputs for the communication/radar signal transmitter 1 10 are: an input frequency modulated sawtooth wave 140, i.e. a linear frequency modulated signal or a chirp signal with a tunable delay time Tdo, and communication data 150.

According to some embodiments herein, the transmitter further comprises a single sideband mixer configured to generate the chirped FSK modulated signal. Figure 2 shows the transmitter 1 10 with an example single sideband mixer 1 14.

As shown in Figure 2, the single sideband mixer 1 14 comprises a first 90-degree hybrid 210 configured to receive the input sawtooth wave 140 and generate quadrature local oscillator signals LO.

The single sideband mixer 1 14 further comprises two pairs of switchers S1 , S2 coupled to outputs of the first 90-degree hybrid 210.

The single sideband mixer 1 14 further comprises two double side band mixers 220 coupled to the outputs of the first 90-degree hybrid 210 through the two pairs of switchers S1 , S2. The states of the two pairs of switchers S1 , S2 are controlled by the encoded communication data to exchange phases of the quadrature local oscillator signals to drive the two double side band mixers 220.

The single sideband mixer 1 14 further comprises a second 90-degree hybrid 230 configured to receive an intermediate frequency IF signal and generate quadrature IF signals for the two double side band mixers 220.

The single sideband mixer 1 14 further comprises a power combiner 240 coupled to outputs of the two double side band mixers 220 to combine the outputs of the two double side band mixers and thereby generate the chirped FSK modulated signal 120.

The transmitter may further comprise a power amplifier PA 116 to amplifier the chirped FSK modulated signal and an antenna 118 to transmit the chirped FSK modulated signal.

In the following, the principle of generating the chirped FSK modulated signal 120 in the transmitter 1 10 will be explained in detail.

The frequency modulated sawtooth signal 140, as shown in Figure 3, has a fixed amplitude. Its frequency is changed periodically. The period of the sawtooth wave is T _sw . The frequency sweep bandwidth is B _sw . The frequency sloop, i.e., chirp-rate, is defined as k= Bsw Tsw. The instantaneous frequency, f _R + ^ t, is called as a radar frequency. The IF signal input to the mixer has a constant frequency f IF- The radar frequency is much larger than the IF frequency f IF- For instance, the radar frequency may be around 60 GHz or even above 100 GHz, while an IF frequency may be 10 MHz. The tunable delay Tdo controls the starting time of the sawtooth wave 140 for the anti-interference purpose which will be explained later.

The communication data 150 to be transmitted is encoded firstly in the encoder 1 12, for example by an 8-bit-to- 10-bit (8b/10b) encoder. The "8b/10b" encoding maps 8-bit words to 10-bit symbols, to make the number of "1 " equal to the number of "0" in the encoded data. The details of 8b/10b encoder and decoder may be found in prior art.

The encoded data controls the switchers S1 and S2 either "on" or "off", to generate chirped FSK pulses via the single sideband mixer 1 14. As described above, this mixer 1 14 may comprise two 90 hybrids 210, 230, two double side band (DSB) mixers 220, a power combiner 240, as well as the switchers S1 and S2 to exchange the phases (±90°) of the sawtooth wave 140, acting as LO signals, for the two DSB mixers 220.

In the following, it is explained how the phase of the sawtooth wave changes the frequency of the output signal.

The input sawtooth wave and the input IF wave can be represented by equations: y _R {t) = A _R cos (2n (f _R t + t ² ) + <p _R )

Vi _F it) = A _IF cos(2nf _IF t + <p _IF )

where <p _R and <p _IF are the phase of the sawtooth and IF wave, respectively; A _R and A _IF are amplitudes of two waves.

A single DSB mixer's output is given by

y(t) = { _cos [ _27r (f _R + t + f _IF ) t + <p _R + cp _IF ] + cos [ n (f _R + t - f _IF ) t + <p _R - cp _IF ]} (1 )

It can be seen from the above equation, for the mixing component at frequency C+†IF), the phase is equal to <p _R + <p _IF ; while, for the mixing component at frequency k.

(fR+- t-fiF), the phase is equal to <p _R — <p _IF . When combinin two identical DSB mixers' output, the mixing component at frequency c-f IF) can be

either enhanced, i.e. adding in-phase or suppressed, i.e. adding anti-phase by controlling phase <p _R and <p _IF .

When the switcher S1 is "on" and S2 is "off", the mixer generates a chirped FSK pulse with a frequency equal to (fR+— c-fiF). The mixing component at frequency (f R+— t-f IF) has a phase equal to q>R- (piF=90°-90°=0 for the up DSB mixer, and C R- (piF=0°-0°=0 for the k

lower DSB mixer. Therefore, the frequency components (fR+- t-f ) obtained from two DSB mixers are added in-phase at the output of the power combiner 240. Simultaneously, the k

DSB mixer generates also mixing component at frequency (fR+— C+†IF). The component at frequency (f _R +^ t+fi _F ) has a phase equal to (PR+(PIF=90°+90°=180 ⁰ for the up DSB mixer, and q>R+ (piF=0 ⁰ +0°=0 ⁰ for the lower DSB mixer, therefore, the components at frequency k

(f _R +- t+fi _F ) obtained from two DSB mixers are added anti-phase at the output of the power combiner 240, consequently, the component (f _R +^ t+f| _F ) is suppressed.

When the switcher S1 is "off" and S2 is "on", the phases of the sawtooth wave 140 for the two DSB mixers 220 are exchanged, which results in the mixing components at k

frequency (f _R +- t+fiF) from two DSB mixers are added in-phase, and the mixing components at frequency (†R+^ t-f IF) are added anti-phase. Thus, at the output of the

k

power combine 240, the mixing component at frequency (fR+- £+fiF) is dominated, the component at frequency (†R+^ t-f IF) is suppressed.

The communication data "0" and "1 " are represented by a chirped FSK pulses at frequency t+fiF), respectively. For example, a data sequence

1 10101010010001 1 101 1 101010010010 1010, will be represented by a FSK pulse sequence, as shown in Figure 4. The chirped FSK pulse sequence will be amplified and transmitted via an antenna.

Figure 5 shows an example of the radar receiver 131 . For a conventional FMCW radar, the reflected signal is a sawtooth wave too, the frequency difference Af = kr between the transmitted and received sawtooth waves is related to the time-of-flight, τ, i.e., the two-way travel time of the microwave from a radar to a reflector. The distance R between the radar and the reflector is obtained, R = ^ΑΛ where, c is the speed of light in the air. If the reflector and radar moves relatively, the relative speed can also be found by looking at the frequency spectrum of the reflect signal over several consecutive periods.

The radar receiver 131 comprises an image reject mixer (I MR) 501 configured to mix the received chirped FSK modulated signal with the input sawtooth wave 140.

The radar receiver further comprises a low pass filter 502, a power detector PD 503, an analog-to-digital converter ADC 504 and a baseband processor BB 505. The encoded communication data is removed by averaging frequencies of FSK pulses in time domain in the baseband processor 505.

In the following, how to demodulate the reflected chirped FSK modulated signal and remove the communication data will be explained. For the integrated communication and radar system 100 according to the embodiments herein, the reflected chirped FSK modulated signal contains the FSK signal too, as shown in Figure 6. By down-convert mixing the sawtooth wave 140 and the reflected chirped FSK modulated signal, the linear frequency modulation, i.e. frequency ramp, disappears, but the FSK signal remains. The IF frequency for the / ^' -th pulse if , / ^' =1 ,2,3.., are given by

If = Af ± f _IF (2)

The average of Af is given by

Ifave = - f _1F )} (3)

where / and m are the number of pulse at frequency Af - f _IF and Af + f _IF , respectively, and n=l+m is total number of pulses. When l=m, yield

lfave = f (4)

After the 8b/10b encoding, l=m, and the frequency difference Af is equal to the average of if of the pulses.

Af + f _IF is always large than 0, but Af - f _IF may be either larger or less than 0. The "sign" of the second term Af - f _IF in the right side of the equation (3) need to be known. A so-called image reject mixer (IRM) 501 , as shown in Figure 7, may be used to solve the problem of "sign". The IRM 501 comprises two DSB mixers 701 , 702, two 90 hybrids 703, 704. One input to IRM 501 is the sawtooth wave 140 at frequency acting as a LO

k.

signal. Another input is the received reflection wave at frequency f _R + - t— Af ± f _IF , acting as the RF signal. The IRM 501 has two outputs, i.e., the up/lower sideband output USB/LSB. When the RF frequency is larger than the LO frequency, the up sideband has IF signal and the lower sideband has no output signal. When the RF frequency is smaller than the LO frequency, the lower sideband has IF signal and the up sideband has not output.

If the average frequency Af is larger than f _IF , see Figure 8(a), -Af + f _IF < o. "sign" of the term (Af - f _IF ) is negative. The up sideband output has no IF component signal; while, the lower sideband output has output, because of (Af ± f _IF ) > o, as shown in Figure 8(b). After low-pass filtering, analog-to-digital converting (ADC), as well as estimating frequency of each pulses, the Af _ave is obtained by average. if _a v _e = Af when l=m, f _IF < Af _ave (5a) However, if the average frequency Af is smaller than f _IF , see Figure 9(a), -Af + f _IF > o . "sign" of the term -Af + f _IF is positive. The up sideband output has an I F signal at frequency—Af + f _IF . Simultaneously, the lower sideband output has an I F signal at

5 frequency Af + f _IP , as shown in Figure 9(b) and 9(c). The Af _ave is obtained by the

difference of the average frequency for the lower sideband output and the average frequency for the up sideband output:

Afave = 7∑ W + ftp) - 4 when l=m, f _IF > Af _ave (5b)

10 The integrated wireless communication and radar system receives not only the reflected signal, but also communication signal from another radar integrated wireless communication and radar system, as shown in Figure 10(a). The communication signal maybe a potential interferer for the radar measurement. The received communication signal and the reflected signal has a relative phase 7>τ second. If T _s is very small, the

15 frequency difference between the communication and reflection signals is probably within the I F band of the radar receiver, then, the communication signal will interfere the radar receiver.

Even though the relative phase T _s , of the received communication signal is unchangeable, the delay time of the input sawtooth wave Tdo may be tuned, see Figure

20 10(b). The relative phase between the reflected signal and received communication signal Tdo+T-Ts may be increased, so that the frequency difference between the communication signal and the reflected signal is outside the I F band of the radar receiver, consequently, the interference signal may be filtered out by a low-pass filter. By the way, such kind of interference exists between automotive FMCW radars, even though the

25 transmitted/received radar signal is not a chirped FSK modulated signal.

Figure 1 1 shows an example embodiment for the communication receiver 132 together with the input signals.

The received chirped FSK is demodulated by a down-converting mixer 1102 with a 30 synchronized sawtooth wave as a LO, as shown in Figure 1 1 , to remove the linear

frequency modulation. The obtained FSK signal is then send to a FSK demodulator 1 104.

The synchronization of the received communication signal and the sawtooth wave is realized by tuning delay time Td which is the relative phase of the sawtooth wave as a LO. The delay time Td is obtained from the spectrum of the down-converted I F signal by a so- called synchronizer 1106. The details of synchronization scheme for the chirped FSK communication signal may be found in prior art. For example, form a spectrum obtained from the down-converted I F signal, a measured center frequency f _c is obtained. The center frequency fc is related to the time delay Td, and the relative phase (r _s + τ) for the received communication signal, which may be expressed as:

f _c = k(T _d - T - T _s ) (6)

Td may be adjusted until the frequency difference between the received

communication signal and the synchronized LO signal reaches the desired intermediated frequency (I F). After mixing with the synchronized LO signal, the frequency chirp is removed. Namely, the chirped FSK pulses become a conventional FSK pulses which will be send to the FSK demodulator 1 104.

Figure 12 shows an example embodiment of the FSK demodulator 1 104. The FSK demodulator 1 104 comprises two DSB mixers, the up one 1201 and the lower one 1202, as well as two bandpass filters BPF 1203, 1204, two low pass filters LPF 1205, 1206. Those two DSB mixers 1201 /1202 are driven by two LO signals at frequencies of f _c +f IF and fc-fiF, separately. After low-pass filtering, the outputs from the two DSB mixers are sent to a power detector 1207. "0" and "1 " data are obtained from either the up or the lower DSB mixer and send to the decoder 133, for example an 8b/10b decoder, to decode and get the communication data transmitted from another integrated communication and radar system.

A method performed in the integrated wireless communication and radar system 100 for operating radar and communication mode simultaneously will be described with reference to Figure 13. The method comprises the following actions, which actions may be performed in any suitable order.

Action 1301

The integrated wireless communication and radar system 100 encodes

communication data represented by a binary sequence such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data.

Action 1302

The integrated wireless communication and radar system 100 generates a chirped FSK modulated signal from the encoded communication data and a chirp radar signal, i.e. a sawtooth wave.

Action 1303 The integrated wireless communication and radar system 100 transmits the chirped FSK modulated signal for both communication and radar measurement.

Action 1304

The integrated wireless communication and radar system 100 receives a first chirped FSK modulated signal reflected from a reflector and a second chirped FSK modulated signal transmitted from the other wireless communication and radar system.

Action 1305

The integrated wireless communication and radar system 100 generates a radar signal for distance and/or speed measurement in a radar receiver by filtering-out the communication signal in the first chirped FSK modulated signal.

Action 1306

The integrated wireless communication and radar system 100 obtains the communication data in a communication receiver by demodulating the second chirped FSK modulated signal.

To summarize, in the integrated wireless communication and radar system 100 according to the embodiments herein, a wireless communication system using chirped FSK modulation and a FMCW radar system are integrated in a single system. A chirped FSK modulated signal is used for both communication and radar measurement.

Communication data represented by a binary sequence is encoded in the encoder 1 12, e.g. an 8-bit to 10-bit encoder, such that a number of data with value "1 " is equal to a number of data with value "0" in the encoded communication data. The chirped FSK modulated signal is generated from the encoded communication data and a chirp radar signal in the single sideband mixer 1 14. Consequently, the FSK modulated signal may be removed in the radar receiver 131 by averaging the FSK pulse's frequencies in time domain. In the communication receiver 132, the chirped FSK modulated signal may be demodulated by mixing the received chirped FSK signal with a sawtooth wave

synchronized to the received chirped FSK modulated signal, and then using a

conventional FSK demodulator 1 104. The communication data may be then obtained after decoding, e.g. an 8-bit to 10-bit decoding in the decoder 133.

In this way, the wireless communication and radar functions may work

simultaneously, thus, the communication capability, e.g. data rate, is improved, comparing with the time-domain duplex solution. While, the distance/speed measurements can be carried out continuously. In the radar receiver 131 , the wireless communication signal is removed in digital domain with a simple average algorithm. This solution is much simpler than the transceiver with circularly polarized microwave. Furthermore, both wireless communication transceiver and radar sensor operate in the same frequency band, so they may share the same packaging, antennas, such as one antenna 1 18 for transmitter 1 10, one antenna 136 for both radar and communication receivers 131 , 132, as well as a part of microwave circuits, e.g., a power amplifier 1 16 for transmitter 1 10, a low noise amplifier 135 for both radar and communication receivers 131 , 132 etc..

The transmitter 1 10 and the integrated wireless communication and radar system 100 according to embodiments herein are applicable in an electronic device for vehicle-to- vehicle communication and distance/speed measurements, for unmanned aerial vehicles- to-vehicle, e.g. drone communication and distance/speed measurements, or in sensors, for instance to monitor temperature/smoke/moisture, in health-care and wearable healthcare system for obtaining and transmitting vital signs from sensors to repositories or other units. Figure 14 shows an electronic device 1400 comprising an integrated wireless communication and radar system 100 according to embodiments herein. The electronic device 1400 may be any distance/speed sensor and communication nodes. The electronic device 1400 may further comprise a Memory 1420 and a Processing unit 1430. When using the word "comprise" or "comprising" it shall be interpreted as non- limiting, i.e. meaning "consist at least of".

The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used.

Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appended claims.